Assuming you didn't want it to be super portable, I'd go ahead and just drop a few 4x4's in the ground(optional, of course) and then start building up from there. So long as your frame work is level, you could quite literally just pull a large piece of netting over the cage and be solid. Only thing I would consider is having extra/loose netting at either end of the cage. If you do, you can use reballs and have a fairly easy time collecting them as they will almost all just be chilling bunched up in the net.
CFOA/PSP Certified Referee