Your's is the ultimate coop for its size. I just finished my 6 x 6 coop, and as everyone forewarned, I wish it was bigger. Already I'm planning in my mind what the "next" coop will be and you've built it.
You used upright treated 4 x 4's the same as I. If I had it to do over again, I would poor concrete about 2 ft deep into round cardboard forms for support piers and embed bolts in each. Then I would attach the floor to the concrete piers and use standard 2 x 4 walls, rather than having any 4 x 4's in the walls.
Based on your experience, would you change the way you did this aspect of your coop? Again, I love your coop!