I disagree. Yes you learn a lot when you build you own car, unless you have the skills to do it right you may buy yourself more problems than you gain. The SCCA rules are often difficult to understand and honestly confusing at best. I beleive it's better to start out with an already built car, race it for a few years, and then after being in the club for a couple of years tackle a build at a later date if you really want to.
Even starting with a free donor car, a friend of mine spent 11K on a build to end up with a marginally performing car because the funds wouldn't permit buying the best of anything. After he was done, he may have been able to get 6K for the car. Over time he improved the car, and it ended up being quite quick, but by then close to 20K was spent. Had he started with the 6K built car, he would have had an extra 4K to spend on improvements. I have seen front running winning cars in ITA sell for 10-12K.
In my case, I bought fully caged showroom stock (SSC) race car with a winning history for $1800, spent a couple of thousand on some cheap suspension and upgrades to convert it to ITA, and went racing.
To me a scratch build when the finished product is worth pennies on the dollar keeps you from spending money on the most important thing in racing, track time.
YMMV