Interesting space. I agree it seems a bit dark in the pictures.
One thing I know from my own flock is that they like to sunbathe in the morning. I think that it would make a great coop with some mods if you were able to make the entire area the coop and make the run coming off the gated end perhaps. Never heard chickens complain about to much space. Just a thought.
Which side of the structure is the gate on?