Frame up builds are lofty projects to embark on. Unless you:
-have the experience to be hands on (stripping your own frame, through the removal of components and cutting off any/all unwanted metals), then assembling and final race preparation of the car
-an open checkbook to fund it (as said here 30-50k),
-have the background to be a serious contender, and a buddy in the business who is willing to let you help with the project,
-or If you are the "keep up with the Joneses" type,
I highly recommend you avoid it. I had a couple of guys bring me a near new trucks (way long ago) to transform into a ground up pre-runner build. After stripping all of the wiring, interior comforts, front and rear clips, and stock suspension, they realized the scope of the work they requested was a bit large. They weren't sure in the beginning the difference between what they wanted, and what they needed. In the end, both wished they would have scaled it back a notch or two, and just bolted onto an already capable platform, the necessary performance mods to achieve the desired end result.
The biggest benefit to ground up builds, is that you can ultimately save a few hundred pounds (which could cost you 20 bucks a pound to shed). You can still succeed in winning without going that far if you invest in your suspension, and high end components. Throw a crappy set of shocks on our car, or any lead contenders car, and suddenly victories are no more.
Ground up builds are for two groups of enthusiasts: The serious racer who will be able to exploit the lighter chassis, and the guy willing to pay interest to have what the other racers have. If you can fund it, AND feel good about it in the end, when it becomes a money pit, then by all means, jump on in!