You can buy radio systems today that are inexpensive and reliable... it's not worth the cost or the effort to build your own. Years ago, modellers built their own radios from kits or schematics because there were no inexpensive, mass-produced systems, but now they are plentiful. As Bruce said... no club will want you flying your home-brew TX at their field... and that will be a big problem if you are really interested in RC planes.