I wanted a more portable (and more demonstrably period) loom than the typical inkle loom, so I decided to build myself a box loom. I based my design on the loom made by Spanish Peacock.
The plans I drafted can be found here. If I had it to do over again, I would make the towers where the rollers attach taller, to give more clearance over the edges of the box, as can be seen in the Spanish Peacock design. Still, it works well enough to get the job done.