Here is my case for a Raspberry Pi Zero W when being used as a dongle computer. I have also left an opening in the top so a heat sink can be added if needed.
The holes are for M3 bolts and will cut their own thread into the bottom of the case. It is necessary to slightly widen the holes on the pi zero for this to fit as the stock holes are for M2.5.
The small ridges in the middle of the bottom plate are for the hooks of a male USB plug to latch into before the unit is sandwiched together. When I was happy with the positioning and wiring I glued the USB plug to the plastic casing.
IMPORTANT: Be sure to cover the side of the USB plug touching the pi in electrical tape so it does not short anything out.
Novaspirit Tech has done an awesome blog post on the ins and outs of getting this working with wiring and programming info found here: