It is very spacious inside. If you check out the website with the specs the way the roosts are set up and leave lots of space for many chickens to roost yet lots of floor space. There are no window in it yet, which I do plan to do before summer for extra air flow. But as Hondo58 said the ventilation is at the top of the roof, you can't see it, and there is a skylight which makes it quite bright in the coop, I was actually a bit concerned the chickens might not want to lay because it was quite bright but that doesn't seem to be a problem.
Also, I do plan to build a run as well, but my chickens free range in my backyard all day and will continue to free range for the most part even after I have a run built. I let them out around 8am, and the don't go back into the coop except to lay until dusk, even the other day when it was pooring down rain they didn't go inside the coop, Plus, I was comparing the size of this to what we were looking at purchasing online that stated it would fit 8 chickens and this is much larger inside!