I have been busy with some other things that have kept me away from electronics projects for quite a while. Now I can get back to them, but realize I need some boxes to put them in. I have 3D printed some simple ones a while ago, I will redo the design to make them fit the way I have been building my projects now. Most of my designs use modules that I etch or route. For these I buy copper clad boards that are usually 100 mm wide. This is one of the standard widths availibale cheaply through eBay or other suppliers. One standard size I use is 100 x 70 mm. Going with that as a default I designed a clam shell case, that has two identical parts, that you join together with a few screws. I want to be able to simply add modules without having to drill holes in the case.
I also made a set that fits one of the standard 50 x 70 mm perf boards I use sometime. This one only has 4 internal slots long with the ones on the ends.I made the mounting holes to fit 3 mm screws. They are tight but I was able to self tap without too much problem. Depending on printer settings and filament I might have to run a drill bit or a tap through the holes to clean them up.
For those interested I have added the .stl files to the dropbox I have for the storage boxes from a previous post.