My husband put a board up across the top of the brooder box last night, so they could roost.
All but one of 11 did roost on that board all night. The other roosted on the edge of the brooder box. (Way thinner than the 1x4 board)
Then he let me clean that poopy mess up today.

(I clean everything chicken-related anyway, but that was especially messy!)
He’s right… and you’re right. That is not a sustainable arrangement at their age & poop tonnage!

Tonight will be their first night in the coop.
Just to make myself feel better, and to not feel so bad for them… I did add an extra, lower roost with vices (because it’s temporary), that I know for a fact they can all jump to… it will also enable them to roost higher, if they want, even the ones that aren’t great at flying yet.
They’re all 6 weeks old tomorrow.
I also closed the windows in the coop, so they can feel more insulated & safe. Here in Florida, we do have quite a few things that go bump in the night. Tonight will be their first experience of that.
Thanks to everyone for your feedback!