Marc is sure right about that!
I put a 450kW unit on the roof of a lab building and it involved the structure, vibration, and a host of other issues. They even had to coordinate the generator testing schedule with the lab's experiments because the vibration was enough even through the isolators to disturb the mixtures that they were working on.
Subsequent maintenance was a nightmare working on a generator in the rain and winter on the roof; not to mention that fact that they kept getting visits from the local authorities whenever it ran because the sound traveled to houses over a block away since the genset was on the roof.
Oh, and the Fire Department would only accept it if it was natural gas. No way were they going to buy off on a rooftop fire that could drip diesel fuel down from the roof of a burning building.
