welcome to the forum
just a few pointers there are basicly two cars/books now the old ron chapman £250 mk1/2 escort based "locost" car and its varients and then there is the newer chris gibbs sierra based "haynes roadster" car almost everyone here are roadster owner builders and suppliers
there has just been a few mx5 roadster updates/tweeks that have just come out so you now have the option of using mazda mx5 parts or donor.
if you want to build the old style chassis locostbuilders would be a good site to ask Q. on the other hand if your thinking of going down the newer sierra/mx5 based build then you are in the right place