Our SU was rich, because the original principal had talked them into buying land to expand the college. It was criticised as unethical, but in fact he did them a huge favour. Not only did they own their own SU building and the land underneath it, but the college had to pay them ground rent for land that some college buildings were on. Paying rent to the college for the SU building is not good because they can always lose the lease if the college wants the building and/or the land, but it is the norm everywhere else.