Cut six squares from your plywood sheets. Each square should measure 16 inches by16 inches. Trim your wooden dowels into four pieces 15 inches long.
Place one of the plywood squares on to the flat work surface. Cover the bottom of one of the dowels with wood glue. Press it to one corner of the plywood sheet. Repeat with the remaining wood dowels. Turn the project over and fire to nails into the plywood corners to further anchor the wooden dowels.
Apply a thin line of wood glue to the edge of the plywood square. Press another piece of plywood to the edge, so that it stands vertical to the one laid in Step 2. Secure the edge by firing nails into the wooden beams in the corners. Repeat with the remaining pieces until a wooden cube is formed. Allow all the wood glue to dry completely.
Cover the top and sides of the upholstery box with spray adhesive. Cover all the surfaces with spray adhesive. Carefully wrap the surfaces with batting. Gently pull the excess batting to the bottom of the ottoman. Secure the batting to the bottom of the ottoman by stapling around the perimeter of the bottom. Trim away any excess batting with a pair of sharp scissors. Add extra layers of batting until the ottoman reaches the desired thickness.
Unroll the upholstery fabric on to a self-healing mat. Be sure to unroll the fabric face down on the work surface. Use a straight edge to trace out a 20 inch by 20 inch square on the back of the fabric using a piece of the chalk. Cut out the square with a rotary cutter. Repeat a few more times, until five squares are cut.
Place one fabric square face down on the center of the work space. Fold the bottom edge up about half an inch. Take the next square of fabric, fold the edge up half an inch, and place it face down along the bottom edge of the center square. Use straight pins to pin the fabric in place along the folds.
Repeat step three until a square is pinned to each edge of the center square. Thread the sewing machine with upholstery thread in a coordinating color. Sew along the pinned edges, removing the pins as you go.
Slide the fabric over the top of the ottoman, inside out. Pin the open edges of the squares together along the edges of the ottoman. Slide the fabric off of the ottoman.
Sew along the pinned edges, removing the pins as you go. Be sure to stop sewing about four inches before the bottom. You should now have a sleeve you can fit over the ottoman. Slide the fabric sleeve in place.
Wrap the excess fabric around to the bottom of the ottoman frame. Staple around the perimeter of the bottom as you did with batting. Thread a curved upholstery needle with your thread and sew up the openings at the bottom of each side. Sew using small, even stitches.