Say the width is 8in, you cut in 4in on each length and the desired height say 8in again. So when you have a 8ft length of ply you measure down 8in and then cut out 4in x 3/4(the thickness) of the ply I used and continue to do that every 8in on the length of ply apart from the 4 pieces you have for the overall frame. When you have all the lengths cut you can connect them by pushing the cut out slots from each length together that will eventually have all the boxes. Hopefully you'll understand what I'm trying to explain.