I think the idea with metal roofs is they are supposed to shed (they are very popular in areas that get a lot of snow). Inherent in the idea is you have to design them so they don't unload on the entry/exit paths and on sidewalks or so it would seem to me.
But what do I know, I just shovel the stuff.
I think Bruce is right, and I don't shovel the stuff as often as I should.
The VT slaters said the way THEY detail roofs up Nawth is with a flat strip (I forget what it's called, of course) running along the eaves so the snow doesn't form ice dams OR get stuck-- it just falls off. And if you have half a damn brain, you keep the walkways and driveways the hell away from areas where the snow -- and rain--is going to fall.
That's called good design.
Ralph