At present Raspberry Pi Zeros are unobtainable where I live, and I really wanted one for a specific job. I had an old one, so old it doesn't have WiFi. I found a cheap Ethernet adapter that uses the SPI interface (with instructions here: https://www.raspberrypi-spy.co.uk/2020/05/adding-ethernet-to-a-pi-zero/ )

The Pi and adapter need some protection so I designed a case to house them both. Although the design has parameters, it is specific to the exact adapter board. I've included the source file as well as the .stl in case anyone wants to adjust it for a different adapter board. (This is my first attempt with FreeCAD so there are probably better ways to do the task than what I've done.)

The adapter specs say that it can draw more 3.3V current than the Pi can supply so I got a tiny Buck converter that will give up to 3A at 3.3V. That just sits in the case alongside the Pi's GPIO pins. I've put a bit of electrical insulating tape over the nearby pins to make sure there won't be an accidental short circuit.

Also included is a 3D model of the adapter board. I found that useful to make sure the housing case would be the right size. There's a model of a Pi Zero here https://www.printables.com/model/202605-raspberry-pi-zero-w 

I found some small screws in my box of bits to fasten the two boards onto the mounting posts. The posts are sized to fit those screws - the mounting method is not important, but it is important to secure the boards and prevent any wires making false or dangerous connections.

The holes for the plugs are fairly large because during testing I was using USB and HDMI adapters which have big plastic bits that need to clear the case to seat firmly in the sockets. FreeCAD makes it quite easy to change the sizes of these bits - but I've not tested what happens with parameter alterations so there could be unexpected side-effects!