It's nothing to be taken lightly, I had a metal cooler crushed by sliding roof snow one year. When I got it chiseled out of the avalanche, it looked like it had been hit by a truck! The snow compresses when it dumps like that, and is literally like concrete. Even a 10' x 12' roof with snow only 6" deep can weigh several thousand pounds.
People get fooled even when looking at fluid water and the weight that amounts to.
Ah yes, brings to mind the ice that came off the Man Porch the year of SNOWmahgedon...I love snow...I repeat, I love snow but even I had my fill 2013/2014 winter.

Jan 1 2014...this was the sheets of ice that were under the snow on the Man Porch roof!
Pressure of the weight of the snows above, melts the snow beneath and then it freezes...into much more compacted ICE

Dec 2013 - Winter is not even HALF over
So like when the snow is pulled off the roof so the buildings do not collapse...
Where does one pull more roof snow when it is threatening to go higher than the ROOF of the building?
We had a wet summer, every three days it rained...so winter came and instead of rain, it fell as snow...every three days or so...

December 2013 - we literally ran out of places to put snow and we have five acres!
Mr. St. Higgins' range
Here comes Rick with another bucket!
I can count our blessings...having a tractor and a snow bucket...blessings abound!

I had to roof rake 200 feet of double sided 8 foot canopy roofs every three days or so...thank frig the Parking Building has replaced some of these canopies for vintage vehicle storage. Never again shall I have the task of that many roofs needing clearing off...earn my extra slices of pie that winter.

Fixins loved the up high running doggy ledges...

Snow kept coming right on into May... 
I threatened to sell snow cones to the tourists going by in the spring (yeller ones?)...took until June to see the piles gone...
I love snow and still do...but 2013/2014 was a tad much even for me.
Doggone & Chicken UP!
Tara Lee Higgins
Higgins Rat Ranch Conservation Farm, Alberta, Canada