Your coop is lovely! Although you are not a carpenter (by trade) - you're quite handy! I like the rustic/natural looking wood siding better than painted or stained.
I do have a suggestion or two. If you fill the coop with wood chips/shavings for bedding, you'll want to add a lip at least 6" high around the trap door so all the shavings don't get kicked out.
Rain gutters are excellent. I have one, but it doesn't go into a barrel since there's not enough runoff to keep one full. The downspout just drains onto a flagstone and off into the flowerbeds that surround my coop. Rain barrels are simple to make from a plastic trash can.
Other members have mentioned venting, and you've addressed that - so I'm not gonna go there.
The chickens will roost and poop all over the nest boxes. If you run your roosts longwise in the coop over the nest boxes, add a poop board just at the top height of the nest boxes. Cover it with vinyl flooring or a few coats of paint. Most of the pooping happens at night and not only will this make coop cleaning easier, it will fix the problem of keeping the hens off the nest boxes. This will also give you more roosting space for your birds. My roosts are at window height and that way I can easily see into the coop to check on everyone. I also think they enjoy the view! 
Have fun!
