Could anyone tell me how I could create an autonomous erle-copter that can navigate my university campus, using motion planning algorithms, for example PRM and how can I create a 3d occupancy grid?
Erle-Copter is not designed to fly in indoor environments. You will need integrate some sensors to be able to detect the environment.
There are some projects to do that. Check out this video:
could you tell me what type of sensors you used & from where I can buy them online?
the sensors that we use are listed in our docs: http://docs.erlerobotics.com/brains/additional_devices