We have done the plastic walls for many haunts as well. Currently, we are using lighter weight black plastic for the inner walls and we use a staple gun to attach to the ceiling (of a painted, finished garage, so not the same as at a school). Duct taping the bottom section to the floor keeps each area separated for different lighting effects, which is also easier if the plastic goes to the ceiling. Duct taping the top sections helps keep the staples from pulling through, but this is usually not necessary until after a few years of use. I just double, triple or wad up the top as I staple.

Previously we used duct tape to hold the top up, but this didn't work well in our really cold garage. However, the duct tape sticks to the plastic and to itself well, so sometimes we would make "duct tape ties", from two strips of (about foot long) tape taped to each side of the top and just a little to each other before folding each piece of the tape over on itself and then tieing them over an exposed beam (different garage!). That sounds a lot like the rope method, it's Quick and it's reusable, nothing sticky to wreck your plastic.