Hi there,
I have a few pointers having looked into this alot and owning a Westfield for a couple of years.
Main point is that with a kit it will cost you way more to build than to buy something already finished. The spec of my Westfield would have cost me about £18k to build - I picked it up 2nd hand (factory built) 7 years old with 15k miles on it for £8k.
You also need to consider your skill set - some kits like the Westfield need nothing more than an average toolkit and skills to assemble, other more niche ones require welding skills etc.
A really useful website is
http://www.locostbuilders.co.uk - there is lots of scratch built stuff on here.
If you are talking about scratch building something that is a whole new ball game and has many many problems associated with it. My brother in law (the above mentioned Rodney) is building a Costin Roadster from scratch. This is a car designed by Frank Costin (brother of Mike Costin of Cosworth) the problem is the car never made it into production all that exists is drawings, a spaceframe prototype and one beta test car. Through contact with various people he has managed to get hold off a part finished chassis and one of only 3 sets of bodywork that were ever made. Some of the big hurdles he has had to cross so far include:
Welding additional tubes into the chassis to properly triangulate it
Working out where the engine is going to sit exactly in the chassis and fabricating engine mounts to suit
Having a windscreen made (not cheap!)
Working out all the suspension geometry (not easy!)
How to package the exhaust to pass IVA test in a mid engined car
How to mount the body onto the chassis
I could go on and on, his project has been running about 5 years now and he is just at the stage where he has a rolling chassis, granted his funds are limited but lots of the stuff at the moment is design and fabrication, the expensive bits are yet to come.
If I were in your position I'd get hold of a couple of kitcar magazines and get along to a few shows and see what's what.
For what its worth I sold my Westfield as it was too impractical - now I know you would think - of course its impractical - but however much so you 'think' it is - its worse. Something like that would make a great 3rd car - but not a 2nd IMO.
Good luck if you do decide to start a project!