I created this to hold my son's Pokémon dice.  It took a few revisions to get it how we liked it, but I think this version is pretty cool. It uses 4 2x10mm for each side. 

This can be printed with a single filament printer.  When printing the Top case, open both the top and Pikachu in your slicer to make sure they align perfectly.  Then save the g-code for the Pikachu (no skirting).  

Next, you save the g-code for the Top of the case.  You will need to enable Z-Hop and set it at 0.5mm-0.6mm.  This will allow the extruder to raise over the Pikachu during the print. 

After that, you print the Pikachu file.  After printing, don't touch your bed, just change to your filament, and print the top.