Tom,
As a Fire Officer, what I'd be looking at is damage to the structural members of the building.
As in Roof Trusses, Framing of the walls and anywhere else where the strength of the total building could be compromised.
A big part of this equation comes down to what the roofing material is made from, heavier materials like concrete tiles score a minus 5 (-5) here and We would close it off before the whole roof collapses. [Linked Image]