Building over flat roof

[SunsetSongster]

Hello. Does anyone have any experience of building over a flat roof and the cost involved? Our kitchen and entrance are in a single storey section of our house. I think it's original and assume the foundations are ok to build on as all the other houses on our small street have similar extensions. Any guide on the cost would be appreciated.
Ideally we would also do a small two storey extension as well to increase the available size. Anyone know if it would be advisable to do this in stages - get some space now and more later. Thanks.

Best bet is to get a builder or 2 around to have a look, or ask your neighbours who have already done what you're thinking of doing?

you need to ask your neighbours who have had it done. they may have needed to fortify the foundations as part of the work, but also consult a builder as any past work only needed to comply with whatever building regs were in force at the time of the work and it is possible there may be stricter rules now.

You will need to expose the foundations to prove to building control they can cope structurally. There are other issues such as is the wall already double skin (should be).

You will need an architect and also structural engineer in most likelihood but it helps that others have done the same

Thanks for the replies. I realised as I was writing it I should just ask the neighbours! I'm think one of them actuslly did the work themselves rather than buying it extended. Any ideas on costs if it were ok?