That's a fine looking coop. I'm sure you are interested in maintaining the aesthetics of it. You could build a knee wall as Tony suggests, and use the same shingles as on the coop. Since you already have the top wired you wouldn't need to completely enclose the roof. I suspect the corrugated panels would withstand quite a snow load with just occassional scraping with a push broom. If in doubt you could build a leanto style roof with plenty of pitch. Not sure how this might look but the panels come in shades of brown to match everything else.