[MrForbes]

1/4 to 1/2" plywood usually works ok, although you need to provide some extra bracing under the battery unless it's right at the edge of the robot. Pegboard is not very strong....plywood is stronger. If you want to get fancy, you can use plastic or metal, but you might find that plywood gives you more stiffness for the weight, and is easy to attach stuff to, and the insulating is a good thing as well. It's not quite as "high tech" looking as other materials, for whatever that is worth.