The critical thing about the ceiling is not so much that it keeps the rain out (which I have to admit is nice), but rather that it has these amazingly convenient steel cables wired into it at periodic intervals. Look up and look closely, eventually you will be able to see these dark black cables hanging up there waiting for you to use them. The ones running down the center of the commons have smooth metal rings hanging in them, and thus require no modification. The ones on the north and south of the building are just bare loops of steel cable and thus you will want to put in a metal saddle to protect the rope. If you do not do this, there is a finite probability that the cable will saw through the rope you are about to put there and kill lots of people as 2 tons of equipment fall on their heads.