I'm also in your neck of the woods and converted a lofted shed for my first coop. I had to cut so much ventilation into it that it looked like swiss cheese when I was done...and a secure (rabbit wire) screen door was necessary to keep it cool enough during the summer. Lots of lessons learned with that project, like the importance of eaves to keep the rain from blowing in the windows (my prebuilt shed basically has no overhang from the roof). The learning came in handy with coop #2, which was purpose-built.