Covering the top is entirely up to your firemarshal and what kind of fire department services your event. To have a covered top, generally everyone feels more comfortable with fire trucks and personel on site during the even seconds from being able to hook up and enter a building to evacuate people. Not down the street with a 20 minute responce time. This may be no problem as a campus might have their own?
The justification for a covered top is that it keeps the fog and haze contained that once out of the structure there is no visibility issues to exit. But, a fire marshal may just say no because of the availability of a sprinkler system. In some cases we can't even put a decorative half roof on a facade as it might cover 32 SF of the sprinkler systems function.
Other things you can do to make up for it are not hard, is have an exit, even an actor entry every 50 lineal feet through the maze. Have fire extinguishers in each room and more out on the behind the scenes. The patrons don't necessarily know these all lead to the outside corridor around the whole haunt but all the actors do.
A maze can be pulled off with 60 single sided walls costing $30 new painted. So, $2,000 there, everything else in the begining years, you try to get donated in exchange for free note of being a sponsor such as the fire extinguishers provided by ABC fire supply. Same for electrical harness and sound equipment where you may be lacking. $1250 to $2500 event insurance (unless the campus policy already covers this)
In any advertising and announcements, I would refrain from glorifying that this scary event benefits a theatrical endevor, even though it does. It should be on the fine print at the site but not the reason for the season. You will only end up with half as many show up if it is prejudged as some venue they normally would not attend like a play. In other words, you are entering an opportunity to introduce the mass public to theater and attending your plays but, they came to see a haunted house if you get my drift.
I know a bunch of theatrical types are going to say this isn't so, but, it is. There is nothing wrong with a haunted theatrical offering but, advertising as such can be a turn off to the non academic and that is who a majority of the customers are that will come from miles away for something to do.
60 and 80 miles from here I have just such a scenario. A haunt that is 20,000 SF that has everything going for it and been doing it for more than 20 years but their public service announcement says it benefits a theater organization. They see 2800 per year. The other is in a rural setting and hardly advertises and sees 8,000 patrons per year having only been there 8 years. Then a highly theatrical scene driven haunt I know sees 25,000 and it only has the name of a haunt and a story of a haunt. In fact is is a long standing boy scout organization. Many of these are in towns census wise less than 500 proper.
In a way, saying it is for a charity or a greater good in todays consumer world means it isn't great because all the money goes to the charity. The would be patron wants to pay for a good experience, not 20 percent of an experience being offered and 80 percent absconded with. Or at least this is the perception. Only a 50 year old might understand the donation part. So no reason to confuse them, just get them there and they will like it.
Another fabulous post from the U.S.Department of Wild Imaginings, now in spectaclar stereo, sponsored by the Adhesives and Sealants Council, suggesting ways to stick things together since the 1800s. Not fabulous in a gay way. Your results may vary. Illinois residents add 8% sales tax. These posts have been made by professional post makers, do not try this type of posting on your own without extensive training, lovely assistants and a trusty clown horn.