If its at all possible I would build it. Then like was said, you know every in and out of that car. I have been into bikes for a long time and built them from the ground up as well and I cant tell you how many bikes I have bought that were "almost" complete to find a friggen nightmare to deal with. I have seen some of the worst rigged up wiring and put together stuff that you would not believe. In my opinion, another good thing to owning a car that you built, is that when something does goes wrong you know where to look. You are not chasing a bunch of someone elses screw ups trying to fix a small problem.