Hmmm, a lot to process. Our plans were on hold due to budget/inflation (and more, below), but I appreciate some of your cost saving measures. I just need to do more research on materials before commenting.
Regarding tops/protection, our primary predator seems to be hawks. There are a pair that circle the general area daily. Coyote are also in the area (hear them at night, sometimes) so we need to protect against them. And we need to keep rats out.
That said, despite the hawks, we are rethinking our needs - in part because of budget, in part because all of our neighbors free range. As such, we've been free ranging our chickens across our property as well (over an acre). This has been going mostly well... we are down one chicken, but its possible the goofball just got lost and taken in by another neighbor. One of our neighbors have never lost a chicken to a hawk, but has a sizable contingent of roosters keeping watch.
All this to say, with the rising cost of materials, it's become hard to justify building them such a compound when free ranging seems viable.