Keep us updated as you progress! Another thing I would do differently is to document my coop construction for my coop page. I only had pics from the end stages. And anything you do will be helpful for others!!!
That is my first thought: predator proofing. I'm sure you could use the shed, but I don't know how secure it would be once you add windows and ventilation. And don't forget about chicken math! It'd be difficult to add on if - who am I kidding - WHEN you get more chickens.
However, you have it...