After that: look at the roof for rust, lifted panels, or daylight coming through. Open and close every door and window to make sure nothing is warped or sticking. Check the base of the walls and corners for signs of rot or water damage. And look underneath the building if you can. That'll tell you a lot about how it was sitting and whether the ground underneath was doing it any favors.
If you're buying used from a private seller, ask how long it's been on the property, whether it's ever been moved, and what it's been sitting on. A building that's been on bare dirt for five years is a different story than one that's been on gravel blocks since day one.
