The icon’s not a bad idea. Seeing a sort of difference for ‘minor’ and ‘major’ damage would be pretty neat to see, but I don’t really know what variables would control the distinction at this point. What if you could control when and where the damage icon/health bar/etc. shows up? Maybe it only shows up in the building view mode, or if you click the structure. I don’t think clicking buildings should be the only way to check, though, as it feels like it’d get too micro-manage-y.
But being able to select where the icon appears could be useful–if you have a long road with houses on either side, you could instruct the icon to appear over each roof, or in front of the structure in case they have radically different heights and it gets hard to see or discern them.