Hi OP,
Just done the drop to the guided bus for eldest DS. I haven't looked at the books for a while so just scanned through briefly as a refresher. Beginner's Guide to Chickens, Raising Chickens for Eggs and Meat are pretty comprehensive incl what to do if a hen needs to be put down. Keeping Chickens by Vivian Head is excellent and very detailed but doesn't mention end of life. I would recommend 1 of the first ones and Keeping Chickens. The others are interesting but possibly not as comprehensive.
I think its really great that you are looking to keep hens! I'm an enthusiastic hen keeper so I'm afraid I can waffle on and on and on. I started with 2 hens and a second hand set up from my neighbour when she was moving, and now I have between 13-16 hens at any time - chickens are addictive! I would also say that there is no way that I wouldn't have my Girls and I would recommend hen keeping to anyone.
But there is more work to keep hens than you would first think although its not every single day. Plus as the other poster said they poo - alot - and will eat all your grass or plants unless you manage the situation. But despite this, having had hens I would never ever now buy or eat eggs or chicken that weren't free range. The eggs from my garden hens are far superior than any you buy in the supermarket, but for me, knowing that my hens get to live natural, happy lives where they can have daylight, fresh air, places to run about, scratch, dig, fresh food and water etc etc makes all the difference. That type of life is what you can taste in the eggs.
There is alot to find out though about keeping chickens and I'd just mention things that took me a few years to find out (sometimes the hard way).
I don't know what type or size house you've had left for you or if its a plastic or wooden one. What I would say is that if its wooden before you bring in any hens - replace the roof if its felt, as felt can harbour parasites that will prey on your hens. Onduline roof sheets (not that expensive from DIY store) are much better and helps deter red mite by not giving them places to hide in the roof.
Irrespective of what roof it has or if its wooden or plastic, I would recommend you disinfect the house with a product called Poultry Shield, and if it were me I'd also fumigate it with a smoker. You can get red mite killers that fumigate like ones you would use if you had pests in your house or greenhouse. Then you can 'paint' the interior walls and perches etc with a white vinegar solution - its smelly but a good deterrent. Also as other poster said use red mite powder (Diatomaceous Earth) on walls, perches and any nooks or crannys.
It may sound over the top but you don't know why the previous owners left that coop. It might be that they just won't be keeping chickens anymore, or it might be that they have had pests and felt it was better to just leave the coop and get a new one. Prevention is far better than cure.
You can get the above online. Or check out Farm and Pet or Flyte So Fancy - they sell alot of products other than just coops and runs. Alot of the things they sell you can get elsewhere on internet and also google local Farm Supply or Countryside Stores as they are usually alot cheaper. Half the battle is knowing what to look for.
The previous poster gave you very sound advice so I'll try not to repeat what was said.
Other things I might add is if you have an uncovered outdoor run (mine is open air fenced in by chicken wire and gates), I would suggest you thinking about an automatic door opener for the coop. The door opener (depending on what you get) will open and close the coop door either on a timer and/or by light sensor. There are a number out there - I use one called Chicken Guard which has a timer and sensor.
It basically means that I'm not getting up at dawn to let the hens out and trudging down the garden at dusk to put them to bed. It also means that I can go out for the day and not worry, or if I ask neighbours to mind the hens if on holiday, they don't have to do antisocial hours either! New hens may take a while to get used to going to bed, so be prepared you will have to put them to bed in the coop for a few nights till they get the idea.
My NDN had a large completely covered walk in run with 3 hens with the coop inside. She could therefore use a cheaper wooden house open all the time, as it was protected from the elements, and if she was going away overnight etc she didn't need to worry about putting hens away or asking anyone. She also had part of her lawn fenced and would let the hens out every so often for limited 'grass time'. Anything longer than a couple of days she would ask me to go in.
What will you do if you want to go away? You do need to ask yourself this, no matter what set up you use. Chickens cannot be left completely for days on end - eggs and corn will still need to be done and water and feed checked and topped up. Will your neighbours 'hen sit'? Mine do, will yours??
If you have an open air run as I do, you need to make sure that there are also protected places for the hens to go in cold or bad weather. We have 15 hens so I've got a pretty large enclosure (I used to completely free range but changed to protect my vegetable patch) but you wouldn't need that with just a few. But need for shade, shelter, grit, protected feed and water areas for when weather is very hot, or cold, wet etc are still the same if you've got 3 or 50.
Chickens will climb, jump, fly (unless you clip wing feathers on one wing - its quite easy and painless - like cutting your nails), dig and scratch - its all natural behaviour. We have an old raised bed filled with sand for dust bathing (although they still dig out dusty hollows themselves - any run you have with natural ground will become a moonscape - don't believe the photos of coops sat in permanent enclosures of grass - the hens will eat anything). You also might want to consider wood chip as a base for your run - it needs to be hardwood chip not bark to avoid respiratory problems. But in a small area it gives a easily cleanable surface you can just hose down and helps prevent the ground becoming boggy when its wet, plus they can scratch about.
Coops - if wooden I recommend Flyte so Fancy and Littleacre for solid materials, ease of use and durability. Or Smith Sectional Housing. Yes I know you've got a coop already but its worth taking a look at these websites as it will give you good ideas of what is out there and how you can adapt what you have.
After couple of years of a cheap 2nd hand coop that I needed to repaint every year and was warping, I splashed out on a FSF Granary which is pretty good as I can climb into it, remove nestbox and has a removable tarp on the floor for ease of cleaning.
But I've also got 2 secondhand Littleacre coops - the equivalent of a 2 hen one off my neighbour - its still going strong 7 years on and I recently got a larger Littleacre coop for free off Freecycle. You can get alot of stuff second hand or free if you look - it doesnt have to cost the earth. The larger coop is a 6-8 hen Stamford and we put it on wheels to make it easy to move. Littleacre use Onduline. I don't find pull out floors that easy in a coop as large as the Stamford - coops which allow you to open it up as much as possible are alot better.
I use the Stamford when I'm introducing new hens into the flock.
Runs - you can get panels you put together (see Smith's Sectional or Littleacre), or pre-made runs - or do what I did a combo of Panels in places but mainly chickenwire on posts.
The other thing I eventually got also was an Omlet mobile fencing - its basically netting on metal stakes which you push into the ground. I use it for when I want the hens out of their enclosure and onto my lawn. If you want to change the ground they are on around a coop, it would also be handy for that. Its not that tall but the hens don't go through. The only note of caution I would say is its designed to keep chickens in, not to keep foxes or dogs out. A few months after first getting the Omlet fencing one of our dogs decided to go in to help herself to scratch feed. She ended up completely wrapped up in the fencing, pinned to the ground by the stakes, several of which had severely stabbed her as she panicked and flailed around. I had to cut her out of the fencing, and she ended up having surgery.
I didn't use the Omlet fencing for some time, but I have used it now for several years and never had that problem again. It does its job very well of keeping hens in and I would recommend it, but if you have dogs do bear in mind the above cautionary tale.
Feeders and Drinkers - at the end of the day your hens need access to feed during the day and you need to ensure feed is protected from vermin, and plenty of fresh clean water. I bought what I could initially afford or got from Freecycle. All my initial set up was second hand including the hens.
But to recommend:
My neighbour had a robust metal treadle feeder called a Grandpa Feeder for her hens. The small one feeds 6 hens for 10 days (so she was covered for her 3 hens if going away). I didn't have money to begin with but eventually saved up and bought another large one for my girls as they protect the feed from wild birds and vermin. They are expensive but worth it - I've never seen one second hand.
Drinkers - Tripod drinkers are good. We have many hens so I use several. Tripods will keep the dish away from the ground and have a big tank (useful if you don't want to fill up every day - hens drink alot especially when warm). But I find them a pain in the butt to clean out as you can't scrub inside and difficult to defrost when the water has frozen. So I eventually also bought 2 plastic lidded bucket style drinkers as you can hang them or put them on a stand, and the lids take off easily for cleaning. I tend to clean and disinfect mine with a Miltons solution as it also kills algae. When the water freezes I just take lids off and pour in kettle of boiled water to defrost.
Hens - I think if you get ex farm hens that is brilliant. Go through an organised Hen rescue. Bear in mind they will have patchy or even no feathers at first. Hens kept too intensively eat their own and the feathers of others - thats one of the reasons why I think intensive farming of chickens is so cruel. They will need extra protection from elements - its cold when you are nude! but will soon refeather over time.
But you also need to realise that the farm is getting rid of them because they are coming to the end of reliable egg production. Farm chickens are all hybrids (I have hybrids layers but not rescues) - that is they have been purposely bred to reliably and constantly lay eggs. Hybrid hens lay the most eggs in their first year, then second year still laying but not as many, then by 3rd year they lay alot less frequently and egg shells may not be of such great quality or strength (although you can feed supplements). Farms often get rid of chickens around 18 months. Hybrids also do not live as long as pure breed chickens. It can be anything from 3-4 years (although I have two matriarch hens that are 6 years old) typically. This is because being bred to lay intensively throughout the year they just don't have a long life span. Pure Breed chickens can live up to 10 years in contrast but never lay as many eggs which are averaged out over their lifespan more evenly.
Plus alot of pure breeds don't lay in winter so their bodies rest. Even hybrids lay less over the winter with shorter days but they will still lay.
So rescue chickens might not give you as many eggs, but at least you know you have given them a life worth living after being shut away in a barn. My friend has always had rescue hens and would never consider getting them any other way. I thought about it, but also really wanted reliable eggs so went via Point of Lay supplier.
There's alot to consider, I would advise read up as much as you can, join chicken and poultry forums and research. If you can speak to people who have hens and see their set ups all the better. Then if you still want chickens (and I would definitely recommend them), you will have a much better idea about what you want and can manage.
Good luck, and sorry I've waffled quite alot!