BitsyB, would the clear or tinted polycarbonate sheets, placed at an angle, be enough to bear the snow weight where you are? We got ours at Home Depot. We built small "trusses" for the pen roof and screwed the panels to the trusses for stability. We don't get the same amount of snow down here, though! It has held up through 50 mph + winds, though.
https://www.backyardchickens.com/web/viewblog.php?id=12029-coop_01
https://www.backyardchickens.com/web/viewblog.php?id=12029-coop_01