1. Flip box upside down and screw one caster into each of its four corners.
2. Measure top of box, then cut plywood to make lid (or have a store like Lowe's cut it). Sand edges.
3. Place foam on floor. Place lid on top of foam and cut foam to fit lid.
4. Spread batting on floor, and place box lid and foam on top of batting. Cut batting three inches larger than lid and foam on all sides.
5. Lay out fabric facedown on floor. Center batting on fabric, then place foam and lid on batting.
6. Create cushion by pulling batting and fabric taut over one edge of lid, stapling to secure. Repeat on remaining sides.
7. When all edges are stapled, trim any excess fabric.
8. Fit lid to top of box.
Adapted from Design*Sponge at Home, by Grace Bonney (Artisan). Copyright (c) 2011.