Good advice re: roosts. So, the inside foot print, including the feed room is 8 x 10, not counting that fantastic front overhang?
If I had the time, this is what I'd do:
1. Be sure to get it raised up off the ground so that moisture doesn't rot out the floor joists.
2. Gut it, and bleach it.
3. Cut in some windows. Awning style, hinged at the top so they can be left open when it rains/snows. Be sure to have 1/2" hdw cloth firmly attached under the windows.
3A. Ventilate, ventilate, ventilate: multi level. Louvers are nice b/c they allow air flow while restricting rain/snow. Plan on at least 1 s.f./bird or 10% of floor space, which ever number is greater. My coop in zone 4B is 10 x 12. When ALL possible ventilation, including doors and windows are opened, I have 64 s.f.!
4. Remove the in coop feed room. Use some of the overhang space to add a feed room, if you would like to have one in your coop area. (who wouldn't, if they had the space!)
5. Paint the interior to help prevent rot and to lighten it up. Apply vinyl or black jack to the floor, and run it up 12" on each wall.
6. Build outside access nest boxes. If you are in an extremely cold climate, make the nest boxes part of the floor foot print. If your weather is a bit warmer, you might like to make them a bump out style.
7. I would turn that nice overhang into a predator proof covered run/sunroom to give the flock a safe haven if you can't let them out into their regular run early in the morning.