Kudos to you! It sounds like you definitely have your work cut out for you, but that you have a lot of rich resources! I think you could probably charge a little more than $5.00 and people would understand. We're an outdoor haunt (in a cornfield in the middle of nowhere) so I don't know about the roof, your fire safety inspector should come out and see what you have in mind and be able to advise you what your limits are. On the otherhand, a haunted gymnasium sounds like a lot of fun -- I'm thinking of the way sound will travel in there! Very cool. I work at a private university in Texas, but if our Theatre dept. offered a "Haunt 101" I'd sign up in a heart beat. You say the closest pro haunt is 1.5 hrs away, but what is the population base of your area? If marketed correctly, with a good show, I think you'll be surprised at how quickly you can draw a crowd! Sounds like fun! Good luck!
"Enthusiasm is one of the most powerful engines of success. When you do a thing, do it with your might. Put your whole soul into it. Stamp it with your own personality. Be active, be energetic, be enthusiastic and you will accomplish your object. Nothing great was ever achieved without enthusiasm."
~Ralph Waldo Emerson~