You could run the roost from the far wall to the middle of the door space. Put a hinged or removable support right across the inside of the door opening, a support on the far wall, and rest the roost on them. Make sure it won't fall off at the wrong time. We have something like that in a bigger space where the far end of the roost is hinged and the support at the door end is hinged on one end and supported with a rope on the other. Not ideal but we needed more roost when we got more chickens and it works.