Thank you all for the feedback! It is much appreciated!!
Push has come to shove on the interior design. I've been kicking this can down the road so far... so many different set ups that work depending on the individual coop designs, needs and preferences of the people, and so on. I like aspects of dozens of comments, articles, and coop pages... some of which are incompatible with each other.
So. Starting with the known.
The nests go above the bedding.
The poop board goes above the nests.
The roosts go above the poop board.
Allowing at least 8" for deep bedding, at least 12" for nests, absolute minimum height of roosts is 21" above the floor. Almost essential is margin between top of nests and the roosts to make them visually obviously higher... add 3"... making bare minimum of 24".
Much more comfortable to allow 12" for deep bedding, 15" for nests, 6" for visual margin and addition of the option of a poop board. That is 33" from floor to roosts for reasonable minimum if no poop board or except for
Maximum height of roost: birds need head room while on the roosts and clearance for getting on and off the roosts. Minimum for getting off the roosts is 45 degree angle, so horizontal clearance is equal to height of the roosts. Theoretically, they could walk down but they don't. I have a walk in coop with more than 8' of horizontal clearance so roosts could be over my head... nope, I don't want that.
If I have a poop board, I want to use it without bending down.
https://ergoweb.com/work-at-proper-heights/
My elbow is 42" high. 42 minus about 3 inches for the clearance of the tools (leveling system, broom, and screen)... puts my poop board at 40". Which is above the comfortable minimum. Oh, that is 40" above the level of the bedding; not the level of the floor decking... so 52" above the floor. But the bottom of my window is 48" above the floor. Even with a lip around the poop board, I think the PDZ would blow out too much if it is above the bottom of the window -if it is in front window. I'll put it against the west wall so it isn't in front of the window and leave it a range of 4
I don't know the best distance between the poop board and the roost. If it is too high, the poop misses the board. How high that is depends on how wide the poop board is. If it is too low, the roost is in the way of working the poop board.
I think my limiting factor, if I use roosts that aren't easily removable, will be the hand broom I intend to use to clear off the PDZ when completely replacing it. That should be rarely, so this can give if needed. The hand broom has 3" or 4" bristles plus handle, my hand, and a little working room... figure 6" to 8".
Do hens use the poop board to get past another hen on the roosts? I read that long ago but can't remember if the hens do that or if the writer just thought they would. If they do, how close does it need to be? If they don't, would they use a parallel second roost for that purpose?
And, my kids woke up so that is all for now.