The box is built from an openscad module, you can manipulate the size and shape of the box by passing parameters. However, I've really only printed this size. I printed it out of PLA on a Lulzbot mini with .25 layer height.
The lid slides into the box on some rails. There is a small bump on box sides that lines up with a notch in the lid. The lid snaps shut pretty snugly, but isn't so tight that it is hard to open.