My tractor is 4x10 with an open area at ground level and a sheltered area (4x4) above the ground. The sheltered area is where the roosts and nest boxes are. The chicks have been in this tractor for about a month (they are 8 weeks old now). I have a tarp partially enclosing the bottom as a wind break and semishelter. I have had roosts at the ground level for them all this time as well. Two nights ago I saw them parade up the ladder and all roost in the top enclosed area. They repeated again last night. (They are such big girls now.) All this said, I believe they instinctly seek a sheltered, high area for the night where they feel most secure. I am new at this though.