Last week I got two older hens along with their house that was in need of repair. I figured I'd keep them in a horse stall in the barn until I got the house fixed up and they learned where "home" is. The first day there both hens and flew over a 5+ foot wall and escaped through the barn window. One of them I think did get lost in the back pasture, but they were both back at the barn that night to roost on the 5 foot tall window ledge in the barn.
Your set up looks great, but the way. However, the chickens will likely be able to get out unless you put a cover or netting or something over the top.
Since chickens can actually fly fairly well, is it necessary to put ramps leading to the nesting boxes?