1. Spawn any square prop, preferably from PhoeniX's Premium Model Pack for Garry's Mod 10, and freeze it
2. Attach four Wired Thrusters to the bottom of the prop on each corner with a force of 150
3. Attach a Wired Ranger to the bottom of the prop in the center with the range to 1500 (default)
4. Attach a Wired Value with a value of 75-150 on the bottom
5. Attach a Less Than gate from the Logic-Comparison gates
6. Using the Wiring Tool, wire up the components like so:
First Click-->Second Click
Less Than-->Value
Less Than-->Ranger
Thruster-->Less Than
Thruster-->Less Than
Thruster-->Less Than
Thruster-->Less Than
7. To make the prop stable, use the Keep Upright tool on the prop
8. Release the prop and watch it automatically adjust itself to stay at a set distance above the ground, if you want to increase this distance, just increase the value of the Wire Value to whatever you want.