They will be built of leftover scraps, hopefully 1" x 2" or 2" x 2" for support on sides, top, and bottom. They will measure about 3' x 1' x 1' roughly. We will wrap hardware cloth around the outside, stapling it in place. Then a lid, made somehow that the mice can't open it. I have shelving going over the potato box and the sand box that the boxes can sit on.

This is hardware cloth: