Revisiting this topic.
Had a further idea to make it more interesting.
Inevitably its likely that a garrisoned building will, if assaulted by the enemy, be destroyed and the troops hiding in it forced out. However it would be cool if destroyed buildings could then be refortified by a Combat Engineer and used as a garrisonable structure one more time; holes patched up and walls reinforced with sandbags, logs and bracing – essentially “militarizing it”. This “second coming” of the structure would be less strong than the original but would allow a formerly cleared building to be reoccupied by the attacking force that cleared it, or by the defending force stubbornly returning, and likewise allow for structures destroyed before ever even being garrisoned to still see some action.
After being destroyed a second time the structure would become damaged beyond all repair.
This would require 3 versions for buildings (or even 4). Standard how it appears normally; a damaged version when an original is destroyed; a rebuilt version with obvious damage but sandbags etc; and finally a pile of rubble when a rebuilt version is destroyed.
It’ll be fun!