Quote: Did a quick sketch.
If the front 1x6 is a 2x4, the a 1x4 could be added at the 6 inch height. I have several birds that like that 6 inch height.. Note that the risers are not set in the corners but inset a few inches. this allows the birds to sit either facing the wall or to the front. and to not poop on those roosting on the next riser.
Sometimes there are 8 to 10 birds sitting on each roost for warmth.