Paint your ottoman with several light layers of plastic spray paint, allowing for several minutes of dry time between coats. Let the paint dry completely before proceeding.
Hand-sew the ends of two lengths of ribbon to the underside of each corner of your chair cushion.
Turn the milk crate upside-down and set it on top of your chair cushion, matching the edges.
Tie the cushions to the crate with your ribbon. Flip the crate back over to view your finished ottoman.
Cut your plywood to match the dimensions of your box cushions. Paint the plywood to match or complement your cushions.
Drill a pilot hole matching the caster screw size in each of the four corners of the plywood board. Attach the casters to the holes with the included hardware and screws.
Place your newly constructed base on the ground, wheels down. Stack your cushions one by one on top of each other to complete the project.