attach the three 2 x 4 x 2 pieces to the support studs. I used a little 2 x 4 to space the middle rail support in the middle of the box. After you have the three vertical supports. Attach the 2 x 4 x 6 across the top of the three rail supports. Take the plywood, line it up to the top and pencil roughly where the vertical studs are. Then jigsaw the holes out.