Buddy! First of all you need to sit with pen and paper. Draw a diagram of car you want to build with all details... like wheel/steering/power pack etc. The objective of your car is the one which will deceide all these. Once you are done with all the detailed drawing work and specification, go to shop and buy motor, car chesis, wheel. Assemble them and make a normal car first (free running with power supply). Once your car is moving with your intended requirement, buy the RF Transreceiever (Analog/Digital) and attach it to the car with proper connection to all the guiding circuit. Test drive it.......