My dorm had a private bathroom for every two rooms. It was adjoined in the middle. I didn't smoke at the time, but I did try weed the first few times in the dorms. Common procedure for us was go into the bathroom and close the door. Turn on the shower - with very hot water running. Get the room all steamy and turn on the overhead fan. Toke away. Use the toilet paper thing when you exhale. This always worked like a charm.

Of course, this is only if you have private bathrooms.

Otherwise, depending on where you go to school, I would just find some low key place outside to go smoke.