It is strange how many people will shovel their roofs during a snow season because they are worried that the roof may collapse.
I took this video where we placed the roofing material for the entire house on a small roof. All together it was five thousand pounds of material. There is no way that any amount of snow could cause a roof to collapse, however, a possible explanation can be that drains placed toward the middle of the roof can become clogged due to lack of maintenance, and all the water that collects under the snow can become heavy enough to make the roof collapse.
Snow build up is very good for roofs. It acts as an insulator against the freezing cold. The water that comes from the melting snow gets a chance to drain off before it could freeze. If you remove the snow, any water or rain will freeze because there is no snow over that area.