Just be aware that custom build ups, even of stock frames, cost more than buying a complete bike UNLESS you scour the internet for cheap parts. Get your group set in the UK (Wiggle, Ribble, etc.). Look for take-off of bars, stems, seat posts. Find or build cheap wheels. Otherwise the project will be very pricey. It is likely more cost effective to buy a full bike close to what you want and sell the parts you don't like on ebay, replacing them with your preferred items.

Full disclosure requires I say I build up all my bike myself. But I buy lightly used frames and parts to keep the cost down and I build all my own wheels. That is how is has to be done to make any sense.