Hello,
and welcome to Backyard Chickens!!!
So nice to hear you might add on an addition to your flock! Sounds like you have a wonderful flock right now too! So neat to hear you are building a coop for the chickens! Your birds will be so happy!! We had a little red coop at first that we bought that fit about 5 chickens. After we built the new coop that probably fit 10 also had a roosting bar they all moved on to that on and abandoned their little red coop so than we started using the red one for our 8 week old chicks than they got older and we moved them to the one that we built. Some prefer the roosting bars and others sleep in the nesting boxes.

