What Pat said...
This is such a great little coop! It would be a welcome addition to anyone's back yard!
I built a similar coop last Fall for 3 chickens. The indoor part was 4x4, but you'll loose space with the nest box. In a cold climate, I would not put more than 3 chickens in there - it's just not big enough when they have to be locked in for days (or maybe even weeks) on end. I don't know how frequently that might happen for you, but it's pretty darned common around here. We're in a heat wave right now with temps in the 20s (F) and my girls are enjoying some time outside for the first time since Christmas.
And personally, I don't think that it's really big enough for 3 birds, but that's just me. I like to see at least 8-12 sq/ft per bird in genuinely cold climates if it's possible. I know I'm going to take a lot of heat for that comment, but it has paid off for me.
The space under the coop will help decrease the wind tunnel that is going to inevitably occur underneath. It also makes a good storage space. HOWEVER, I am quite positive that critters are going to make it quite cozy for themselves no matter HOW HARD YOU TRY to keep them out. I don't know about you, but having a frightened chipmunk leap out at me while I'm kneeling down in the snow to refill feeders doesn't sound like a great way to start off my day...
If you left that storage space open and available for the run, I recommend VERY deep litter as an insulator. Build the doors (human and chicken) 9-12 inches above the floor so that shavings don't fall out each time the door is opened. If that's not possible, put a removable 1x6 in front of the door, but build your doors tall enough to accomodate. I'd also recommend hard-wiring it for a heat lamp that can be positioned high and operated with a switch. A metal exterior fixture with a ceramic socket is easily sourced at any large hardware store. A small number of chickens will have a difficult time keeping a coop warm using only their body heat (and residual sunlight from the window) in harsh climates. While you're wiring for heat, I'd put in at least one electrical plug for your water dish.
Regardless, the coop walls AND CEILING will need to be insulated and then sealed in with plywood. I'd recommend a higher R rating than simple styrofoam panels if you can do it. Ventilation should be in the gables both on the run side and the back wall. Make them closable for when storms roll through or temps get too cold. Personally, I'd put in more ventilation than this coop shows (3 holes in gable). You can always close it up if it's too much, but finding out that your coop is humid and stinky (and a frostbite trap) and having to cut new vents after you've insulated will be a bummer.
I'd also try to make the window as large as you can, both so your birds can have a view of the great outdoors, but also for the sunlight that it will let in to assist in heating the interior. I particularly like how they have the window/screen set up. Really looks great and super functional.
It's a great looking coop - I especially like how they have painted it inside and out to protect the wood.