We installed bins 4 feet wide, 40 feet down the center of the greenhouse. With a cross-wall of block every 8 feet, we have a total of five 4x8 bins. Since I need access down the center anyway, I didn't lose much growing space to the vermicomposting bins. They could be more narrow, of course. (Their width should relate in some way to efficient use of a 4x8-foot sheet if the lids are to be made of plywood.) The sturdy lids will take any load I put on them; and I have found them a great place to lay out winter construction projects, instruct a class, even set up a winter picnic!