Here's a video with a bit more detail than the photos:
I started by putting 4 4x4 treated posts in the ground to make a 4'x8' rectangle.
Notice, I left the center piece of flooring to stick out a foot on 1 side. That is for the nesting box.
I actually made an annoying mistake during the construction of the flooring. I nailed the floor framing to the outside of the 4x4s rather than running them on the inside of the 4x4s to make the sides flush. It also threw my measurements off since I had the posts separated 4' x 8'. By making this mistake I made the coop 4'3"x8'3" which didn't allow my use standard 8' materials. Luckily, I needed more flooring anyway for the nesting boxes so I didn't bother changing it, but if you are planning to build a coop like this, I would run the floor joysts on the inside of the 4x4 posts.