One note on something not addressed in the above link.
If on-campus living is provided by the college, but it is not available because they are full, then one can claim the full amount of off campus costs incurred. However, to substantiate the claim you need a "letter of non-availability" from the school. This is usually included with the return of the denied housing application. Keep that letter with your tax records forever, just in case you're ever audited on that.
