FIRST has instructions on how to make your own robot sizing box here. I had some extra 3/4 inch plywood though so I decided to use that instead. The only thing I bought were two 18″ x 24″ sheets of plexiglass that I cut to make windows for the box. I cut the plywood into 2 pieces that were 18″ x 18″, two pieces that were 19.5″ x 18″, and the top piece at 19.5″ x 19.5″. Then I cut out the windows a little smaller than my plexiglass pieces and used a router to trim insets to place the windows into. In the end I had this:

The next step was using some construction adhesive to glue in the plexiglass windows and mount the handle to the top piece.

Finally, it was time to assemble the pieces. I used some wood glue and 1.25″ brad nails to put it all together. Plus a few screws on the top help support the weight when lifting the box by the handle. Overall I think it turned out pretty well.