Attic bathroom?

[Ericaceae]

Has anyone put a bathroom in an attic space and could give us a sense of time/cost/practicalities?
Basically we've got one huge attic room that's been converted years ago, boarded out, plastered, electrics, smoke alarms, etc. Hasn't been classified as a "bedroom" because the space is accessed by the original steep and twisty Edwardian staircase (there's not an option to move this and I wouldn't want to rip it out)
We use the space as a games room/kids' hangout, and I want to add a toilet, sink and shower to one of the two smaller storage rooms beside it.
One is above the current bathroom and against the back wall where the soil pipe is, so that seems most sensible, but I don't know what we've have to consider in terms of the boiler and water pressure. Current shower is electric and we've got a combi boiler.
Any ideas or experiences?
@PigletJohn any words of wisdom?

We recently put a bathroom into a room with steep sloping ceilings on both sides. Not an attic but similar in shape. It's an old cottage but this room was in an 80s extension.
To get water pressure into the room we used a pump like this one-
www.screwfix.com/p/salamander-pumps-ct-force-30-pt-regenerative-twin-shower-pump-3-0bar/13779

It was difficult designing it but we are thrilled with the results. How big is your space?

It cost us about £11-£12K. A lot of the stuff came from eBay ex display etc. Cost was mainly labour (£7-8K). Took three weeks.

Sorry when I say a lot I mean specifically -

Roll top Bath (Burlington Harewood slipper bath)
Bath taps (Burlington)
Toilet (Carlton)
Basin (Carlton)
Shower head (30cm Hudson Reed rainfall shower £35 from eBay! - LOVE it!)
Shower taps (Hudson Reed)

Flooring was Luvanto LVT in bleached larch (c. £300). It's brilliant. Water proof, good with our underfloor heating.

If you have a combi boiler then the pressure should be sufficient. However Victorian houses often have narrow waterpipes, which restrict the flow, especially the supply pipe from the stopcock under t pavement into the house.

If this is the original lead one it is a good idea to replace with modern, larger plastic pipe, preferably 32mm, and to run larger pipe all the way to the combi, and from the combi to the bathrooms, and the cold pipe as well, preferably 22mm copper for both hot and cold which is taken off the 32mm plastic so it has enough capacity to supply both at the same time. Your water co may offer a subsidy or free connection if you are replacing lead pipe, it is being phased out for health reasons. If you ask them, they will take a sample of your drinking water and test it for lead content. This must be done before you start work. It's free, so get your request in and join the queue.

Also look at the size of your stopcock(s) and service valves. The modern small type often operated with a screwdriver looked like a great idea when they came on the market, but they restrict flow due to small internal bore, and most are poor quality and tend to leak. This often leads to poor flow in showers and especially bath taps.

Better, full-bore valves are more expensive so plumbers often don't fit them. look out for this if you are having work done, specify them and look to see that you get what you paid for.

A 32mm plastic stopcock is particularly expensive. if it's in the ground you won't see it and it will be much more work changing an undersized one subsequently. The extra cost of larger pipe is relatively small.

Thanks so much, both. Good to get an idea of price. I'm a wee bit at the lead pipe chat, but better the devil we know! It's a couple of year old main bathroom that we've got just now put in by the last owners, so hopefully they've looked at that at the time. Eesht!