I would take some cardboard, lay it out, duck tape together. When you have exactly what you want, then use plywood. Appliance stores are excellent places to get the right size cardboard. Start with the smallest box and add a inch and a haft for each box, all a round.
I went to the link. He wasted a lot of material. All ready he is ready to change it. The nice thing is you can learn from what he did.