My main coop is an old greenhouse. It's not glass, it that wavy fiberglass stuff on a wooden frame.
The things I like about it....
It's big. I never really have to worry about my birds having enough space.
It's tall enough I can walk in. this just makes so many things easier.
it has a dirt/gravel floor. This is my favorite flooring.
the fiberglass panels are easy to cut holes in when I need to modify something. need more ventilation? Just use an ordinary knife and you can cut a hole in the side of the building.
cons....
The fiberglass is old and not so strong in some areas.
It can get warm in the winter.
the roof leaks more as the building ages.
predators could be an issue.
. My building has a shelf running about waist height all around the interior, it's made up of slats. Some of the birds sleep on the shelf, some in the rafters. I also have a pole roost I put in the corner between the two walls that several of them like to sleep on. I put the nest boxes on the floor. I use rubbermaid tubs on their sides and they do just fine for me. I use deep litter, so if a hen decides to lay somewhere not in a box, it's not a big deal. The only issue is crawling back under the shelves in the corner, not always my finest moment trying to get back up!