The walls are 12ft and there is a celing too that is made of 3/8" polycarbonate (lexan). Below is a link that at the 27-28 second mark I launch another robot to the celling. At the national event the celing was only 6' up and we launched another robot so hard off of it that it sheared two bolts that helped keep the ceiling on.
YouTube - Plum VS Plum
I really like then end of this one
Is the large purple motor that drives your rotary weapon brushless?