Insist on a very good home inspection. I'm guessing that 6'5" ceilings are not up to code - if this is an attic or basement conversion and it's not up to code and not legally permitted, you might be made to tear it all out if you buy it ( that's what happens in my state if you buy a home with an unpermitted addition). Be very careful. Also even if legal ceilings they low could make it difficult to resell, the price you pay should at least reflect that.
