Bantams can probably work with a 10" x 10" box, 12" x 12" or 14" for standards, and somewhat larger for large breeds. Here are some pics of the nest boxes I just built yesterday. They are 15 1/2" W x 16" D x 16" tall for the big birds, the little birds, and everything in between.
Sometimes two smaller birds like to climb into one box together, so I made them large enough for that. I added the strip at the top to make the entrance hole a little smaller to make the boxes feel more cozy to the birds.
I also built the walkways / perches large (they extend out from the boxes 12") for the comfort of the birds. The bottoms of each box are removable for cleaning purposes. I am going to go get some bedding for them this evening.
Edited to correct a typo.... Oops!
Sometimes two smaller birds like to climb into one box together, so I made them large enough for that. I added the strip at the top to make the entrance hole a little smaller to make the boxes feel more cozy to the birds.
I also built the walkways / perches large (they extend out from the boxes 12") for the comfort of the birds. The bottoms of each box are removable for cleaning purposes. I am going to go get some bedding for them this evening.


Edited to correct a typo.... Oops!
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