It really depends. If you're a student there, and you're not trespassing (read: forcing your way into a building after hours) you will probably be fine. Most academic buildings are open fairly late, and so long as you're not trying to organize a student/club meeting in a room without scheduling it... I can't think of what issue they would take with you being there. Try not to use anything technological (generators, etc) as backdrops as that might cause some people to call security in a panic.
As for outdoor photos, it should be even easier assuming that your cosplay isn't too edgy/revealing/trashy and you're not drawing scads of attention to yourself and what you're doing. Then again, I suppose it depends on where you're doing the photoshoot. On an empty lawn or against a random building should be more than fine, but if you're trying to use something iconic (a school seal, clocktower, the 50 yard line of their football field...) I could see the University taking a dim view of the shoot, no matter how innocent it may be.
If you're *really* nervous about permits, check the school's site for a Housing, Conferences and Hospitality or Special Events office and ask them about the steps you need to follow for a non-commercial photoshoot. Once they find out that you're not trying to make money off of them, they'll probably handwave you through the process.