I'm getting some silkie chicks and thinking about their housing. They'll be staying the night in a shed that has a large door I'll open and close throughout the day (I also store feed and hay in there), but I want them to be able to get in and out even when the big door is shut, except at night when it will be closed up completely. This is what a pop door is for, right? I'm planning to just cut it out of the larger door and fasten it with hinges and a lock mechanism. But how large should it be for silkies? What if I ever want larger chickens? Thanks!