You can build anything you want, if that's what floats your boat. I've flown with an old timer that likes to build his radios, but he preferred single stick radios that aren't very popular these days.

Two words of caution though: If you want to build a radio system it absolutely MUST comply with the FCC guidelines for RC aircraft radios. And if you want to use that radio at MY club I'm going to want to see a certificate that makes me believe that you aren't going to shoot my plane down while I'm flying.

Second: You will probably end up teaching yourself to fly, since I don't think that thare alot of clubs around that would trust a home made radio. Teaching yourself is certainly doable, but more difficult.

Good luck.