Step 1: What You Need
1/2" plywood: this would all fit in one 4x8 easily. I used scraps lying around.
25" of 2x4, or 50" of 2x2 for the inside support.
15" x 15" of foam (I had 3" around and used that, if I were buying it I'd probably go thinner).
2 cheap 14" IKEA pillow forms for additional padding on top.
Fabric for cover (I had two pretty pillow cases that I used for the top, and bought 1 yard matching fabric for the rest, fabric not pictured).
hinges/1/2" screws for hinges.
screws for building the frame (2" or 3" works fine).
Table saw/miter saw (or whatever you have to cut wood)
Orbital sander or sandpaper