[peterwwillis]

You really don't know that about concrete buildings without inspection, and possibly core sampling of the concrete. You don't know what the true grade of the concrete is or whether it's thick enough depending on loading. And you need to look for signs of common failure modes such as carbonation, chloride penetration, freeze/thaw cycles, alkali-aggregate reactions, etc. Most concrete failures can penetrate the entire slab before showing outward signs. And concrete slabs have 'exploded' from as little as 200C of heat due to trapped water vapor. This assumes it's earthquake-code concrete construction.

A mostly-stone building will be perfectly fine, though :)