I found this cool Roll Top box by http://www.thingiverse.com/Fused3D/designs and tried to design my own square version. It became also a nice calibration tool, the box should be 50x50x100mm when assembled.

I only print in PLA, 0.5mm for the top, bottom, shell and a infill of 30% will do just fine. I used Superglue to stick the left and right side together and used some kitchen oil to grease the sides of the roll-top a bit, works wonders.