I just want to mention that if you're like me (and a majority of people on BYC) you'll get more chickens than what you start out with. Please take that into account. I just got two new chicks and I feel the need to add another run onto the other side of my coop. I always wish I had a bigger coop too, but I feel like the coop is adequate.
My chickens love their run, so I think more run space is more important than more coop space for me. My chickens only go in the coop to eat, sleep and lay. I keep the water in the run and they generally stay outside, even in rain. Anyway, always plan on more chickens (even if you don't get any) and you'll be fine.