We have ours in our barn as well. We remodeled a corner horse stall for them. It is not nearly as big as your area, ours is only 10x10. Our stall walls were 1" boards about 4 foot high. From those we put wire to the ceiling. Since we have a hay mow, we have an actual ceiling in the stall... if we didn't, I would want something there, like you are talking about. This was basically my project and though we had 2 hens a few years ago, I didn't really do much in the stall at that time. We just did the wire and made up a nest box and roost. Unfortunately we only had them a few months before they were caught by foxes while free-ranging. Then we got 6 chicks last year, started them in the house because it was COLD that winter. When it was time to move them out to the barn, I wanted it to be better than it was for the other two. Hubby calls it their jungle gym now.
In the stall I used the manger area for a nest box. It was 3' long so I tried dividing it into 2 boxes. It didn't really make a difference because they all (6 hens) wanted to lay their eggs in the left side, so would either dogpile into it or take turns. I've seen 4 of them in there at one time. I finally took the divider out when I allowed them to hatch some fertile eggs that I bought (another story). There is also a "roof" on that. That wall is the one that faces the center barn aisle, so they like to be up there and watch for me. When they were young, that is where they spent their nights all huddled together.
I built a long "box" on the wall with a roof and with roosts in it for them to sleep in. Silly me! They slept on the roof, even though it was slanted. So I altered that so it was flat and put a removable roost on top to make it easy to clean. I have boards going around 3 sides of the stall at different levels a foot or so from the wall, with the nest box and people door on the 4th side. I also put a window in so that it wasn't as dark. They love to be on the board by the window, looking out, when they come in for the night.
Because I have the room, and I had one girl that got stepped on accidentally and had a sore leg, I put in a 2x4 board ramp from one of the upper levels to the bottom of the nest box (about 2 feet off the floor). All of them use it! They will form a line and come down the ramp and then jump to the floor. After seeing that, I opted to leave it in, especially after seeing posts about so many chickens with hurt legs and feet. My girls don't like flying down from the high places... if a ramp will save them pain and me worry, it is worth it. I even put a small ramp from the highest level to the next one down. Some use that, some don't. (I have added higher boards since I took this video of the ramp.)
I have a chicken door for them in the wall going out to a 15x40' run. That way they can be safe outdoors when I'm busy. They love to free range but I've lost 2 to foxes this summer and don't want to lose any more, so they only get to when I'm going to be out and about. (a fox chased another one while I was in the main aisle and they were with the horses in the lean-to that was attached to the side of the barn! Thankfully, she got away from it.) I have plans to make an additional "pasture" for them that is larger since they hatched out a bunch of chicks and I think I'm going to end up with about 11 birds.
Then one of the best things I put in is a camera that has it's own monitor that is in our living room. My hubby tells people he is watching "chick TV" when he has coffee in the morning while watching the news. It's really handy to know when they come in for the night - I know when to go out and close the chicken door. It is also handy to see what is happening out there. Imagine my surprise when, over the monitor, I heard one of the girls "crow" one morning. It was only one morning but she was sure trying to get it right. We have no rooster! But I have heard one way off in the distance on quiet mornings.
It's a constant work in progress... I add things and move things based on how they are using it or ideas I've had or seen. So, be ready... you will inevitably change some things as time goes on. Have fun setting up house for your girls.