I recently aquired a RPi 2 and a Pi Zero. I tried lego cases and that was fine but i really wanted to fabricate a case for the pi zero. I had no luck finding screws that small in diameter at my big chain hardware stores so I looked at my obsolete electronics to see if I could salvage and repurpose. I had a "Eureka" moment when I spotted the many VGA cables I had been hoarding.
The hole size on the Pi is M2.5 or 2.75mm. The VGA screws will widen the hole very slightly but the screws place quite snugly in the holes.
Step 1: Materials
VGA cables are still easy to find. I had plenty surplus. Use a carpet cutter or something you think can cut through the plastic housing of the cable.
Pull the screw back as far as it will go. Place your blade under the screw and above the housing and cut.
The screw can now be removed easily. Repeat for all the remaining screws.
Now you have essential screws to craft a housing for your Pi to any design you like.