I'm assuming they will go outside during the day and you want them to lay here and sleep here?
How well can the chickens you are considering fly? Some, like Silkies, can't fly. Some really big ones may have troubles, but I've had Orpington, Sussex, Black Australorp, and Rocks that could fly up there and back down if they wanted to. I don't feed mine a real rich diet so mine don't get that big for their breed but that can also have an effect. I find a difference in what they can do and what they will do. If they want to mine can fly really well. if they don't want to they don't fly worth a darn. The trick is making them want to. And giving them enough room so they can spread their wings and fly. In a lot of smaller coops they don't have enough room. That may be your problem, do they have enough room to actually fly.
They can use stairs and hop up. Some barns have pretty steep stairs, some not so steep. If you can use them they should be able to, if they want to. You could use a ladder at maybe a 45 degree angle with rungs every foot or so. They can hop up that. Or provide small platforms three or four feet apart vertically so they can fly from one to another. I don't use ramps but I'd think no steeper than 45 degrees and cleats every foot or so. Would you be doing this inside the barn or cutting a hole for a pop door in the side and giving them access from outside?
Any of these can work if you set it up right but you'll have to train them to use it. That might be keeping them in there for a while before you let them out but you may still have to put them in there at night for a while after you let them out. Of course there are all the practical questions about how convenient it will be for you to manage them up there.
I'm basing some of this response on my experiences growing up on a farm with free ranging chickens. We had some that would lay eggs or even hide a nest and hatch chicks in a 10' high hay loft. They could go up the same stairs we used or they could fly straight up. Some did one, some did the other. As far as I know they all flew down.