The collapsing roof is light as a feather
Solomonic Alchemy 30
Alteration: Substantial
With the quick expenditure of vis and the commanding of a spirit, a sahir is able to make a falling object up to 500 cubic inches in size (such as the roof of a building or a boulder) substantially lighter. Depending on how high an object is, the sahir may not have enough time to cast this spell, but some paranoid (or devious) sahirs have been known to have this spell held by a spirit until the apropriate time.
(Base 15, +2 Substantial, +1 Size)