There are many Quadrotor Projects out there. But, they require a hobbyist to deal with the Frame Designing (Mechanical), a bit of Microcontroller knowledge as well as dealing with the Motor Control (Power Electronics). You may purchase a commercial Radio and a readymade Kit for flying. But, to Do-It-Yourself, is an achievement in itself.
Here is a picture of a Quadrotor designed by Shane Colton using Arduino Pro mini as its flying brain. Shane is a Ph.D Student at Massachusetts Institute of Technology. On being asked about the Project, he replied:
I heard about Arduino some time in 2007/2008 and have used it for a few projects since then. I built the quadrotor for fun / hobby (not related to research). I wanted to build my own (quadrotor) from scratch because I could integrate all the parts onto a single circuit board, and because I like designing the control system myself.