Looks like you have a very good starting point with that shed. A few things to think of. The roost boards. It looks like you are using 1" boards. You might want to consider going with 2X4"s. With a 8' span, if your birds all decide to roost on one board, that board is going to sag, and will need to be replaced sooner, rather than later. 2X4"s hold up waaaay better.
Also, with the roost boards. How far are they from the back wall, and how far apart are they? You want to be 18"s or so from the back wall, and apart from each other. If the roosts are too close to the wall, the chickens will crap all over it. Gotta have a little space. And if the roosts are too close to each other, the unfortunate ones on the lower roost, will receive the same treatment as the back wall.
Think about making the roost boards removable, for cleaning or whatever. In my coop, the roost boards sit in notches, so they are easily removable.
You say you want to keep the feed and water outside. It's a good idea to keep water outside for easy access for the chickens. But give thought to keeping the feed inside the coop. Feed, especially when the chickens get done knocking the feeder around outside may draw rodents. Not to mention the free meal you'll be giving the wild bird population in the area.
Ventilation, of course, will have to be improved. If that was my coop, I would build (If the coop has double doors) A couple of hardware clothed screen doors for it. The more fresh air you can get in there the better.
The Blackjack is a good idea. I used it in my coop, and it's holding up well going on 6yrs.