Saw a 3/4-inch thick piece of plywood into a 16-inch square.
Draw a diagonal line from one corner of the platform to the tip of the opposing corner. Repeat the process with the two remaining corners. Measure 2-inches from the tip of each corner along each marked line towards the middle of the platform and make a mark on each spot.
Drill a 1/8-inch pilot hole through the middle of the platform where the two marked lines intersect.
Sand the edge of each side of the platform until it is smooth. Paint several coats of stain, according to manufacturer’s directions, to the top, bottom and sides of the ottoman platform until the desired shade is achieved.
Center the top plate of a heavy-duty caster over the mark you made earlier at each corner of the platform. Make pencil marks through the screw holes of the caster plate onto the plywood. Drill 1/8-by-1/2-inch deep holes into these marks.
Thread 1/4-by-1/2-inch wood screws into the holes in the caster plates to attach them to the platform. The ottoman platform is complete and ready for the cushion installation.
Cut a piece of foam padding 16-inches square and 8-inches thick.
Spray the top of the ottoman platform generously with adhesive and place the heavy foam padding on it so that it lines up with each side of the platform.
Choose the material to cover the ottoman cushion that suits your needs. Cut a piece of the material that is 28-inches square.
Spread the upholstery material on the floor and place the ottoman, foam side down and lined up with the edges of the material, in the middle.
Pull one side of the material snugly over the side of the platform and use a heavy-duty stapler to attach it to the bottom of the ottoman platform.
Draw the other side of the material over the opposite side of the platform, draw it firmly and staple the edge to the bottom of the platform.
Repeat the process on the other two sides while taking care to keep the seams folded under each other in a neat, straight fashion.
Use the stapler to apply a neat line of staples 1-inch apart around the perimeter of the fabric.
Push a 10-inch upholstery needle through the hole in the bottom of the platform through the foam and fabric in the top of the cushion. Thread one end of heavy upholstery cord through the eye of the needle and tie the other end to the eyelet on the bottom of the button.
Withdraw the needle and pull the cord through the hole in the platform until the button draws down far enough to tuft the material, taking out and smoothing wrinkles. Attach a large button the end of the cord underneath the platform to hold the top button in place.