About the only thing I can find in unincorporated King County is the following. "Poultry, chickens, squab, rabbits, hamsters, nutria, and chinchilla are limited to a maximum of one animal per square foot of structure used to house such animals, up
to a maximum of 2,000 square feet." Department...
I think your coop is great. Your ideas for improvement would help too. I am thinking of building something similar. Except for the base, I think most of it could be constructed with 2x2's and 1x2's to reduce weight. In addition to the changes you suggested, I would make the coop a full four feet...