Wow!! Thanks for all that! You've given a LOT to consider! Can I ask a few follow up questions?
1. (Dumb question alert) In your SUV I'm assuming the boards stick out the back? Can you give tips on safe transport from store to home? I drive an Expedition so have some space especially with seats down but not enough for longer boards not to be completely in.
2. Is there a way to weight the coop or should I cement piers in to the ground in case of hurricanes/storms?
Thanks again for your response!!
I have a Highlander and I can carry eight-foot boards inside my SUV if I lay them up the center and rest them on the console. I don't stack them very high and my store is only a few miles away. I strap them together with a cargo strap to keep them from shifting. If you don't need 8' boards for your design, the also come in stud length, which is 7'6" or so, and 6'. You can also get 10' or 12' and have them cut in two, but the cost for long lumber may make that a more expensive way to buy.
Another option if you have an openable rear window is to put the lumber in and let it extend out the rear window, strapped together and braced so that they can't shift side to side, and with a red flag attached to the part that is hanging out the window. If you have a roof rack, you can strap boards together and then to the roof rack. Any part that extends past the end of your vehicle should have a red flag attached. The twine made available for tying things down at the store is not adequate for any of this. Use appropriate cargo straps.
DO NOT try to carry sheet lumber, panels, or a bunch of boards laid next to each other on a roof rack. That creates an airfoil, like an airplane wing, which often ends badly, with a torn off roof rack or damaged lumber and damage to your and others' vehicles.
If you have ANY doubt that what you are doing is safe, choose another method that you believe actually will be safe.
Our coop is pretty heavy. We used preformed concrete piers on top of well-tamped clay with gravel for fine leveling. The ones we used have a square "hole" in the center for a 4"x4" post and crosses on top for setting 2"x6" boards into as floor joists (same as rafters, but for floors). Our city code required us to have a solid surface floor in our run.
I made ours 8x8 feet because I could carry those dimensions of lumber and I had my plywood floor cut into 4' lengths and used two 4x8' sheets. I put a joist every two feet, which meant five joists, then put down the plywood floor.
I decided on the height I needed to accommodate people and framed the two end walls, one a foot taller than the other so my roof would drain. I used a few boards to hold the end walls up while I took new measurements for the side walls and figured out the angle for the tops of the upright studs on the side walls. Then I framed them and raised them them into place. From there, I measured again, then built the doors to fit the frames I had built into the walls.
I put hardware cloth on three walls and panels on one. One door is for people entrance and one is a 2' high top-hinged door on the lowest corner of the run to enable me to lift it up and rake out the run. There is no footer at that door, so water can run out there, too. I put the water buckets there, on top of gravel. My run still has a tarp instead of a solid roof because I got injured and ran out of nice weather, so the roof panels are sitting in the yard waiting for spring and for me to get my cast off.
If your coop isn't heavy enough to survive high winds, I would cement in your foundation. Videos on how to install a deck are good for seeing how this would work.