If you build any sort of aircraft yourself in the UK, you're going to have to do so under the guidance of an LAA mentor/coach. Otherwise it'll be very, very hard to eventually get a Permit to Fly. These mentors, and the LAA in general, can also help you choose the right kit for you, based on budget, time available, skills you may or may not have (metal, wood, composite?) and so forth.
The LAA also runs a website which hosts a number of forums. As much as I like PPRuNe, for serious questions about kitbuilding I'd go there.
Welcome to the Light Aircraft Association
I can also recommend the following two books:
- Kitplane Construction (Wanttaja)
- Choosing your homebuilt (Armstrong)