Lots of information on quad-rotor (or hex-rotor) vehicles can be found at http://www.mikrokopter.de . All their schematics and source code and a wealth of other information seems to be openly available, so it seems like a very good place to start.
They also sell relevant components and kits at https://www.mikrocontroller.com/ , although it doesn't come cheap. To get a complete kit for a hexacopter, plus everything else you need such as a transmitter, you're probably looking at ~ $2000 AUD.
Here is the complete list of components needed to build a quad-rotor Microkopter, keeping with their existing design. You could of course design or redesign your own from scratch, but still, their list of components gives you a good general example of all the core components that you need.
1 x Main microcontroller motherboard. See http://www.mikrokopter.de/ucwiki/en/FlightCtrlManual
. Their controller board design is based on an ATmega644, and it includes 3-axis accelerometer, 3-axis gyro and provision for a barometric pressure sensor on the board.
4 x Brushless motor controller boards. These switch the significant amounts of power going into the motor coils - these motors can run at about 150 W maximum for continuous operation. See http://www.mikrokopter.de/ucwiki/en/BL-Ctrl_Manual
. The four motors are networked back to the central controller over I2
1 x FTDI interface board or cable for programming and setup and diagnostics
Propellers: 2 x clockwise and 2 x anticlockwise, plus spares. See http://www.mikrokopter.de/ucwiki/Propeller
Structural materials for chassis (small, lightweight model-building aluminium extrusion seems like a good place to start)
Wire, connectors, screws, heatshrink, etc.
1 x radio control receiver module
1 x RC radio transmitter (4 channels)
LiPo battery charger
That the existing designs are not autonomous robotic UAVs… they are radio controlled.