Several months ago I designed a simple case for a small PCB with a simple snap-in mechanism. Out of this model I made this customizable case in OpenSCAD. 

Features:

• adaptable size with automatic lid customization
• lid customization (for example: cutouts for cables or windows)
• selectable screw plates on the bottom for screwing case to something

Check out my Repository for more cases and things https://github.com/andimoto/things