We have a decent sized barn located on the property of home we just purchased. We would like to build a coop inside of it, but the perfect location inside has dimensions that would ultimately become 5ft by 18ft. The roof can be as high as we want it to be. What is the highest that would be useable space for the chickens? The interior of our coop will only be for the roosts, hen boxes, feeding/water - not storage ect. Thanks!