ok so im not sure if this is all buildings in arma3 but when i was playing a little death match with a mate (who was in the larger building in camp maxwell i believe)i lay down and crawled under the building to get to the other side withought him noticing. when i went into 3d person i was able to see in the building and also i was able to aim my gun up through the floor and shoot into the building. i then decided it would be funny to try throw a grenade into the building from underneath the floor. this worked to so im just letting you know that if you go underneath those types of buildings you can shoot through the floor