Snow white - but snow weight? (How much on roof)

I wouldn't worry about it until you get three feet or if it also rains hard and the snow soaks up the water and retains it. My experience is people do more damage with shovels and brooms than than the snow does. Have broken two sky-lites that way when shoveling from a step ladder. If you do get on the roof with snow, remember it's rounded or crowned so it's very easy to come sliding off of it.

Bill