My only advice is, get the largest one you can build or afford. You can’t have too much room, but not enough is a problem. Especially if you live where it gets cold in the winter and your birds are spending the majority of their time indoors.
I just looked and see that you are from TN, so cold weather isn’t a problem for your birds. I’d still go as big as I can.
I just looked and see that you are from TN, so cold weather isn’t a problem for your birds. I’d still go as big as I can.