[MrForbes]

You probably want to make it a little smaller, since robots seem to "grow" during build. We always aim for 26" x 36", yet they end up being just barely able to fit into the sizing box. And if your robot doesn't fit into the sizing box at inspection, you need to modify it so it will fit, or you don't get to put it on the arena floor to play.

Also try to make the top of the robot at least an inch smaller than the bottom. This will make up for the sizing boxes that are not "square". been there, done that