Okay so the roof is held up by the hot air in between the two layers of the roof. It is hot enough to melt 15 centimetres of snow an hour so they dont have to worry about getting wieghted down. WHat happened was the stormy weather lately weakened the top layer and then a panel seperated today. WHen that happened all the hot air gushed upward, that cloud of fog in the picture, and therefore nothing to hold up the roof. the roof then collapsed inside the building.