Can a coop be too large?

[Gtown Farmer]

Thanks for the advice. The coop does have two windows already and I was thinking of putting in a another for added light. I will put in some sort of a vent toward the top.

I'm still concerned about the height of the roof and so few chickens though. I agree that they will not be able to stay warm enough. I think I'll put in a ceiling anyway.

Regarding the concrete floor: I read on this site that concrete was the best option for flooring because it's easiest to keep clean. Also, I live in Upstate NY in a very rural area which means LOTS of foxes, raccoons and opossums. I'm trying to build a little fort knox for them.
Do I really need to seal the concrete? Readers: Please chime in on this.