This tells me the guy on the roof likely played too much call of duty - the tacticool type that gets kicked out of the range for spraying one mag dump after another all over the place.
I haven't seen a picture yet showing the vantage point, but my instinct was how did he miss? Even if with iron sights (don't know yet what he was using), he couldn't ask for a better position, and a rather large stationary target too. Maybe he didn't plan for getting lots of sweat in his eyes. That metal roof would have been cooking him. Then again, don't know how long he was up there.
It's a miracle he wasn't killed.