This is an old pic, pre hardware cloth upgrade. Plan was to install something back left to provide winter roosting. Temps go to around -5C at worst. Winds tend to come from left and back of the picture, so they're protected from brunt of it. They're allowed to roam the garden too.
That entire structure would make a good Open Air style coop with something solid across the bottom 2/3 to 3/4 of the windward end.
Your winter low temperatures seem to be much like mine and my birds did fabulously well even on the worst storms last winter (see here).
Unless you need it as a second layer of predator-proofing, chickens don't really *need* an enclosed coop for the night, especially in a mild climate. They just need to be dry and out of the wind.
