A land or sea based homemade ‘drone’ would have to be large to navigate even moderate terrain or choppy water and the larger the vehicle is the more costly, dangerous and obvious it is. Aerial ‘drones’ on the other hand can be much smaller and unobtrusive. When we refer to drones, what we are really speaking of just a radio controlled vehicle with perhaps some fancy telemetry. Aerial drones come in two basic flavors, fixed wing and multi-copter. I have experience building both as well as automated lawnmowers and snowplows.

Fixed wing
A fixed wing UAV is really a radio control airplane. There are thousands of models available, from palm sized to nearly full scale. Power can come from a battery or even a small scale jet turbine. The best format for a drone would be an inexpensive expanded foam model. These foams can withstand full speed impacts with the ground with really no damage other than a broken propeller (trust me I know). Skillfully built and operated, the fixed wing drone could stay aloft for hours and several thousand feet up. Operation is nearly silent when at altitude.