I'm a big fan of hoop coops and I'm working on a comprehensive guide to building hoop houses for chickens, so I definitely have some thoughts.
Before we talk about hoop coops, I want to point you in a somewhat different direction for your chicken moat/enclosed garden plan. I recently saw a
YouTube video of a couple building a chicken moat around their future orchard. It sounds like you plan to enclose less total area than they did, but I think their video is worth a watch.
I think their design of two lengths of welded wire fencing could work well. They used a graduated field fence (like
this), but you can also use something with tighter spacing if you desired (like
this). The entire thing can be built and supported on t-posts and it looks pretty clean. They did include some cattle panel shade areas which were also supported with t-posts.
This design should also cost less to build. From your rough sketch, it looks like you would need something like 28 cattle panels to construct all four sides of your moat. That adds up - that would cost about $700 just in cattle panels before you've secured them to anything. Another thing to consider with cattle panels is that the spacing between the ribs is pretty big. Chickens and chicken-eating-creatures can get through them if you don't cover them in something with a tighter mesh (like hardware cloth). So, that would add more cost to the project.
If my math is right, you could fence the same area with 240' of field fence or weld wire. You can buy 300 ft of 48" high field fence for ~$150. Want something taller? You can get 100ft of 60" high 2x4 weld wire for
$100 or 72" high 2x4 weld wire for
$130. Just something to think about. If you feel like you need a top to protect your birds or keep your birds in, you could run some type of netting over the top - just consider the potential for snow/ice loads in winter.
Whatever you go with, make sure you also install gates of a sufficient size to get any equipment you might need into the garden area. Don't just think about today - think about the long-term project.
Anyway, thoughts on hoop coops...
Here are the first two hoop coops we built here at the university. We used a frame because these coops need to be mobile, but I would probably use a frame even if I wasn't planning to move them. Cattle panels are very "springy" for lack of a better word. That's part of what gives them structure - the cattle panel wants to straighten out, but it is held in an arch by the frame. I can say these hoop coops have held up to some serious
abuse on our part. They've been picked up by the wind when we forgot to anchor them down and are still in use months later - they just look a little more disheveled. We have had to replace tarps (wire is hard on tarps).
View attachment 2618350
Another thought as I'm remembering the build process...
Cattle panels still move around a decent amount if you just secure the bottom and don't have support for the upper portion. Even after securing the two panels together with hog rings, they still wobbled a lot until we got them secured to the door frame and the rear upright. With your plans, I'm not sure how you would actually support them. You might get to watch them do the "wave" which could be fun.
I may have more thoughts later, but I will leave you with this book for now. Hopefully something in here helps.