I built one out of the t1-11 plywood siding that they put on houses. Built a lightweight 1X2 frame and made it where if a panel got damaged, only that panel had to be replaced. It took one 4X8 sheet. About a $50 investment, and its big enough for a dog to sit on his haunches, with his head up to look out. I don't care for the short ones where they can't even get up and stretch.