you can buy sheets of plastic and plexiglass, usually to whatever specifications you want, as thick or thin as you want. i have also heard of people just taking plastic tote boxes and converting them into growspaces..
you can put them together with caulking, or if you are really ingenious, you can get a heat gun and melt them together....
it's not bad because it's cheap and you can get any size, however it's harder to disguise, much better for stealth if you have a nice looking wooden growdrobe...
shadow