Nothing stopping you from building a car if you want to. I insisted on building my own and wouldn't question doing it again... BUT building my own car from scratch was the point of the project.

If going the fastest for the cheapest- NOW- is your goal, then buying a car is the best way to do that. If you want to spend the time drinking some beers with your buds and build a car from scratch, then take a season (or three) making it competitive, then don't hold back.