ok, here's a step by step walk-through.
1. Think about what shape a box is.
2. Nail some 2x4's together to make that shape
3. Cover top in HDPE, lexan, puckboard, pvc, sloppy joes, etc.
* Seriously, just look at all the boxes in this cult. There are kajillibillifillions. Make a frame to the shape you want, think about height and length, then just go for 'er. If you have the common sense of a doorstop you can build a fucking box. It's like one of the 3 basic shapes in the WORLD