Select cushions for your project. Ottomans are most comfortable to use when they're the same height as the cushion on the chair they are matched with, typically between 15 and 18 inches. Square leftover cushions, whether from a room redo or found at a thrift store, are the easiest to use for this project. Two 6-or 7-inch-deep cushions should suffice.
Cut a piece of plywood to match the dimensions of the cushions. Sand the edges of the plywood, and paint it to match the room's decor. Let the paint dry overnight.
Attach the casters to the bottom corners of the plywood. The casters have predrilled holes and come with the appropriate screws for the project. Lay the plywood down on the workbench, and set a caster at one corner. Use a pencil to make a mark at each screw hole. Repeat at the remaining corners. Drill pilot holes in the plywood for the casters, and screw them into place.
Turn the plywood over so the wheels are in contact with the workbench. Use spray headliner adhesive or contact cement to attach the bottom cushion to the plywood. Follow the instructions on the can. Generally, both surfaces are sprayed and then pressed together to form a bond. Spray or spread the glue to the edges of the plywood and the cushion.
Add weight to the cushion, and let it dry for the recommended time. Use the same glue method to attach the second cushion to the top of the base cushion. Attach any additional cushions in the same way. Wait a day before using the ottoman.