That would make a Fantastic coop! I would replace the bottom row of wood with pressure treated if possible to slow the rot of wood! Wire over the windows is a must! About the door maybe cover the outside by running a 2x2 or 2x4 around the outside of the door? Add a 2x4 inside for a roost and a nest box or 2 then you got yourself a chicken coop! Your shed has a lot of potential! And also....
Keep us posted on your progress!
Nate

Keep us posted on your progress!
Nate