I built up a Beetle-3 drone from spare parts. 

I hand-wired the power distribution, so I wanted a little tray that would secure the wires and provide a flat bottom for calibration and mounting the battery.  It has tie downs for the battery cable and the receiver.

I also needed a little spacer board to raise the FC up so that its connectors wouldn't rub against the frame (no ESC board under it, the ESCs are on the arms).

Written in OpenSCAD for easy modification.