A roof built like these. The ones with the dog houses is pretty close to what I want to do. I would put gates across the front where I can get in and also hang the feeders. The runs would get wider as they get farther into the pasture. I would do a 4x4 post just like that, every other corner. Use 2x6's for roofing members and Simpson ties to attach the 2x6's to the 4x4's. We do 5' spans with the metal all of the time, even the commercial people build with 5' spans. They make special screws for attaching the metal to metal with no underlayment, they call them stitching screws, so there doesn't have to be a support under the horizontal seams.
My home is only built to a 30 lb (HUD) and I think our garage is 20 lb. We get a few inches of snow now and then, I have never seen more than 4". My entire barn was built this way before I moved it for the dairy. That metal is actually stronger than it looks, we have placed 2x4s and plywood on top of the roof and walked on it...I wouldn't want to dance up there though.
Here we get snow say up to two feet we use 2x4 standing on edge every two to four feet with the metal screwed directly to the 2x4 purlins. I was just giving out ideas on how to spend less time in the air and more time on the ground. I have help build and worked in to many pole barns to count. If there is a will there is a way just gotta think it threw
I am all about working on the ground and not the air, especially when the ground isn't level. When I built my chicken coop I had to tie off scaffolding to trees and place it on stacks of lumber to make it level. I also used ladders on top of the scaffolding to reach the roof. I guess you could say that I am pretty good at breaking all of the safety rules but it isn't something that I enjoy. I never did get it painted...
Looks awesome! But I'm curious . . . it looks really high. Is it 2 stories? I love that you have such large openings for air flow. I would love to do that. But, the problem I can see is rain getting in, making the coop floor soggy.