Commercial flat roofs are more likely to accumulate more snow and ice when it’s compared to pitched roofs. if the roof is designed with a high curb all around, it can be the main cause of the snow to park for long term rather than blow away with the wind.
Depending on the sqf of the flat roof, dept of the snow can be a real danger if you ask me. There is big difference in between powder snow and wet moist snow. It may be dry and powder right now but as soon as thaw starts the weight of the snow will multiply. We have seen in the past flat roofs collapsing due to extra weight added on by the wet snow.
It is very important to clear not all but most of it prior to thaw to avoid the structural stress and possibility of structural damage.