chickens perch because its an instinct, to get up and away from danger irregardless of the weather. you will need to put them back in their house. sometimes after a few weeks they will learn to go into their house but sometimes you cant teach them otherwise ( my mother has chickens that she gave up on moving because they sleep 6 metres up in the tree wind, rain snow etc.) however its also possible that they don't feel safe in their house, a predator may have been in there and may still be in there so that should also be checked out