Here's another picture of the coop while it was still under construction with a better view of the pop door. https://www.backyardchickens.com/forum/uploads/15384_im002991.jpg
Meant to tell you that the pop door is to the left of the human door. Its kinda hard to see with the hay around it but if you look closely you can see a hole where the chicks enter. The acted wierded out at first but got used to it very quickly.
We live in Vermont so we get the same weather as you do. We have a pop door that is hinged at the top and held up using a hook and eye. We leave the pop door open all winter. It opens into a secured running pen. We hung heavy plastic over the opening and cut it in strips (like what you would...