I have built a couple cars, nothing too stupid, but done everything myself.
I'd say buy a car that someone has spent all thier money on and wants to bail out of it. If you are patient sit on your money and wait for the right deal to come along.

If you want to say you put some work in it buy a roller that is set-up to your needs / wants and build or install your drivetrain.

As stated you never will come close to getting your money back building nuts and bolts