Just a quick post. I created this simple mount for a RaspberryPi that goes on the ceiling. It has a removable 'globe' to access the Pi. It is about 200 mm across and can be printed on many 3D Printers.
If anyone is building a project which involves mounting a Pi up on the ceiling, this may be of interest.
The 'base' mounts directly to the ceiling and has a large hole to pass cables. There is access to swap micro SD cards. This would require a 90° adapter for the MicroUSB if powering from that port (consider adding a PoE hat).
There should be plenty of room for adding hats on the Pi; and there are also holes around the globe for things like wire pass-through and (potentially) adding ambient lighting to illuminate the ceiling.
Pictured here next to a US smoke detector for scale.