My two cents.
How do you access to clean? Just the end?
If so...
1.Close the end with rat wire and heavy 2x 4 inch fencing to allow air in at all times. Assuming this faces NO into prevailing winds. My storms come from the west, or the north, or north east. My openings face east or south.
2. Move pop door to under laying boxes.
3. Make a human size door across from the nesting boxes you you can reach in and access all areas.
4. Birds need a much larger area to roam during the day. The more the better. My birds roam the whole farm and then roost in the barn rafters. Meaning they learn where home is at night for safety. Others are in smaller enclosures. But always allow 4 sq feet of space per bird. Can you let the birds roam during the day?
5. If yes, eliminate the hole in the floor, and make that part of their outdoor time.
Basically make this into a WOODS type coop. Keep one end very air tight, and keep the far end OPEN AT ALL TIMES. Lack of ventilation will kill the birds fast. Most varieites can adapt to the cold.
6. Have enough roosting space. THe girls will fight over who gets the best spot, and Suzy will sit next to her best friend Dottie. TOp chickens get their preferred spot, usually the highest pole. The lower in the pecking order the more room needed to keep away from the dominant birds.
7. The birds will use the nest boxes for sleeping, so you need to have a way to close it off every night. Cleaning out poo every morning before girls go into lay is annoying, it is more annoying to was poo off the eggs! SUggestion. Remove top two nesting boxes and replace with a roosting pole.
You have done a VERY NICE JOB.
Do try to give them more space to run around on the grass, soon to be dirt.
( My largest woods coop is 12 x 20, and those birds dont need to go outside)
PS. My first coops didnt work out as planned, I adjusted the designs, and build Woods style even if a small coop.
Good luck!!!!