The catch, the building is a linked file. Not much of a catch but there is no equivalent floor in this case. If there was a floor there I'd just check the properties of the floor. Technically if a linked floor matched the perimeter of the building you can still see properties of the linked element if you use the TAB select technique to grab a hold of the element in the link.
...or you could sketch your own a floor around the perimeter pretty quickly. or you could use the area tools. or you could draw a property line. or you could....
Use the Measure Between Two Reference (MbTR) AND check the Chain Option! This will give you a running total as you pick additional points along the perimeter of the building. Here's a quick video demo.
For my money, I'd probably favor a floor. That way when the person who asked you to find out says something like this, "Hey what was that perimeter value again? Sorry I didn't write it down" You can just check the properties of the floor instead of using MbTR again, or flinging your scale at them.