Select one plywood section that measures 1/2-inch by 39-inches tall and 25-inches wide. Measure every 10-inches along the 39-inch side on the left. Attach one L-bracket at each 10-inch location for a total of four L-brackets along the edge.
Select one plywood section that measures 1/2-inch by 39-inches tall and 25-inches wide. Measure every 10-inches along the 39-inch side on the right. Attach one L-bracket at each 10-inch location for a total of four L-brackets along the edge.
Place the 39-inch tall by 30-inch wide sheet of plywood on a flat surface. Line the 39-inch edge of the 39-inch tall by 29-inch wide with the left edge of the 39-by-25-inch section which has the L-brackets on the left side. Drive one screw through each L bracket to create an L-shaped structure.
Place the 39-inch tall by 30-inch wide sheet of plywood on a flat surface. Line the 39-inch edge of the 39-inch tall by 29-inch wide with the right edge of the 39-by-25-inch section which has the L-brackets on the right side. Drive one screw through each L bracket to create a U-shaped structure.
Attach two L-shaped bracket along the end edges of each side in the U-shaped structure. Position each L-shaped bracket 6-inches from each corner. Drive one 1/2-inch screw through each bracket to secure it in place. The top end of the bracket should be flush with the top edge.
Stand the U-shaped structure upward so the L-shaped brackets are on the top. Place the 25-inch by 30-inch plywood section that is 1-inch thick across the top edge. Drive one screw through each bracket to secure the top in place.