The first thing I would check are the steel deck, the joist and the structural beams. They frame the roof and would usually suffer the highest tempertures first. The roof deck can be easily replaced so, it is not major concern other than wanting to keep the building watertight.
If the joist and beams are still straight and not deformed at all, then it is likely the fire was not hot enough to do any damage to them. By checking the extent of paint damage on the steel, a fire investigator can tell the approximate temperature of the fire. Steel will begin to loose some of its strength at tempertures in the range of 700 - 800 degrees, but collapse is a function of both fire duration and loading.
The next step is to check the bearing points where the steel joist and beams bear on the masonry wall. The steel members may not have been heated enough to cause damage to themselves, but they could have expanded enough to push on the wall. Check for wall cracks around the joist plates and beam plates. New cracks should show through the soot on the inside of the wall. A really hot fire will damage the masonry, usually the mortar joints first. The joints will crack and turn powdery. The only solution is replacement.
Here are some temperature indicators of how hot a fire has been as determined by material melting points in degress (F):
Polyethene 230 - 250 F
Lead 620 F
Aluminum Alloys 900 - 1200 F
Glass softens 1100 - 1350 F
Copper 1980 F
This is a start, I'm sure your local fire department would have much of this information.
