How to make a building collapse/explode

I would like to make to where a certain amount of shooting or explosion destroy that part of the wall and then after so much damage i want the building to collapse and the same this with the windows if you shoot them or knife them i want them to shatter. if anybody could help with this i would be great please and thank you!

For windows, model and animate a window shattering, then script it so that if it gets to much damage or what not, it does the animation and delete the colider.

As for the building, that'd be the same thing... Unity (As for as I know) doesn't have the destructable environments that many want... Now, unless you're a great coder and have free time, you could write up some code that destroys those verts and combines them or what not... But yeah... I believe their is not easy way to do this.

Also, check this: http://answers.unity3d.com/questions/30891/destructable-scenery

That might help you further.