Maybe you could add a burning/fire sound, if a building has lost 50% hitpoints... You may find a sound here: https://www.dropbox.com/sh/yfarqen6jsa2asc/AAB-eJU1k6tI-Q21WUy9AE36a?dl=0 (Ambience--> AM_fire.wav) Additionally you can increase the volume, if the building looses more hitpoints...
I like this idea, add some fluff. Why not add a sound effect for sabotaged buildings as well. Which sounds we use is entirely up to anyone, we could use the half life 1 or 2 short circuit sounds and the fire sounds they have.
Yes actually, that's a good idea. A lot of people don't realize something bad is happening unless they are close enough to look at the hp bar of the building. Even then they won't really look at it and know something wrong until it is way too late. Doesn't help that sab smoke gets bugged sometimes and I think a building is going down when it isn't.