Use your saw to cut the plywood into two 6-inch-by-48-inch pieces, one 8-inch-by-48-inch piece, two 7-inch-by-9-inch pieces and one 8-inch-by-10-inch piece. Then cut five 7 1/2-inch-by-6-inch pieces to use as shelves.
Lay the 8-inch-by-48-inch piece of plywood out on the floor. This is the back of your DVD tower case. Then wood glue both 6-inch-by-48-inch pieces in place as the sides of the box. If you're confident with a hammer and nails, you can hammer small nails through the back piece and into the side pieces to increase holding strength.
Center one 7-inch-by-9-inch piece of plywood as the bottom of your box and glue it in place. You may add nails once the glue is dry. Then center the 8-inch-by-10-inch piece over the 7-inch-by-9-inch piece you just installed--this is an extra bottom panel--and glue it in place.
Add the final 7-inch-by-9-inch piece of plywood as the top of the box and glue it in place. You should now have a fully assembled tower case with a long, open front.
Stand the tower case up and, using your pencil and straight edge, draw two straight lines all the way up and down the inside of the left and right panels. One line should be 2 inches in from the open front edge, the other should be 4 inches in, and they should be parallel.
Draw five dots on each line, measuring carefully to ensure they are each 8 inches apart.
Drill through the marked holes with a drill bit the same width as the posts on your shelf holders. Insert shelf holders, then place the shelves you cut previously in the DVD case. You're now ready to stack your DVDs in your homemade case.