My mom likes to have everything aesthetically pleasing--which means that fancy plywood. My sheep shacks are barely borderline. She's only tolerating them because they are temporary. We will be building a barn this spring. And because I offered to pay for part of it, I get to choose how big it is

(I'm going with 16x24.)
As for happiness of chickens....I'm not real familiar with poultry. I worked with them for a month at my petting farm job. However, my sheep were confined for 2.5 months last summer in a dry lot, after being on a pasture their entire lives (as little as 2 weeks to as long as 6 years). I can't tell you if they were happy or unhappy about it. I love my sheep dearly--I spend about an hour after feeding just hanging out with them and watching their behavior. I've raised sheep for seven years now and I was taught all my "sheep skills" by my neighbor who had been raising sheep for almost 80 yrs--mostly range flocks out in South Dakota. They were still acting like their usual selves, so I don't think they were unhappy as I would assume they were happy before. I
do know they were always happy when they saw me coming for food! They would run around the pen and hop and jump and bleat.
I think if a bird is caged and gets their basic needs provided--protection from predators, food, water, and a nest--they will be more than happy because their needs are being met regardless of how much room they have. I know with most livestock if you provide the feed, their space requirements go way down because they don't have to go out and try to find it themselves. I think poultry wouldn't be too far off.