Very lucky that it did not go through the roof - it does not look like it's very strong. I think this shows that the pilot must have done a very good job of arresting the rate of descent for the landing.
It's interesting to note that the rotor RPM must have been very low (as you would expect) when the blades contacted the building - there is comparatively little damage to them.
I hope the pilot bought a lotto ticket that night!
OH