We live in a Victorian house, it's detached but only just, there's a gap of about 6 inches between the house next door. Our houses are a matching pair. We can't do a traditional loft conversion as the pitch of the roof is too low. Our neighbours approached us a couple of weeks about their plan to submit a planning application to raise the roof and add another floor. They've had preliminary drawings done and the idea is to keep very much in the existing style of the house.
They came over to talk to us and we're quite keen to put a planning application in at the same time as even if we don't go ahead with the plan we could sell the house in a year or so with planning in place.
Thing is, I'm quite keen to do the work ourselves. The house isn't our forever house, but it's location is fantastic. Ten minutes from a good station with trains to Victoria taking only 35 mins. The town centre (also a ten min walk) is practical but not terribly pretty but is in the process of going through a £20m programme of improvement including building a Waitrose (yessss 
) The schools are good, we have a lovely large common and wood a five minute walk away and the street itself is fab, a real community feel.
In short the location is perfect but the house isn't. There's no off street parking (and no ability to add any but there are rumours the council is looking at introducing a residents parking scheme - but they've been around and nothing's happened yet) and we have two doubles and a single bedroom and a titchy bathroom.
Adding the extra floor would add two doubles and a shower room up there, we'd lose a bedroom (the single) on the 1st floor to create a large family bathroom, we'd retain 2 other doubles on that floor.
Downstairs we have a living room (approx 13'x13') a slightly smaller dining room which we use as a playroom and beyond that a fairly long kitchen (about 7'x23') which you can fit a table in easily.
We also have a 75' garden.
My question (eventually) is do you think it's worth extending the house? I don't want to make it too top heavy with more bedroom space than living space, given we 're adding a whole floor, the preliminary costs have come in at around £50-60k (for which I'm thinking it's probably around £70k). The house is currently worth around £480k. A 3.5 bed house just up the road sold in March for £492k having been on for £500k but the road it's on isn't nearly as nice and it has only a patio garden. A house similar in size to ours with one extra bedroom (3 doubles and a titchy single) was on recently for £575k. A sold sign has just gone up but I'm not sure what it went for in the end.
Any advice or opinions would be gratefully received.