I had a similar situation last spring when a friend who was helping me build my newest coop decided to install the laminated paneling he was going to use in a camping trailer.
I used 2-by-4's to make a two-level roost with a poop shelf. If I could post photos I would, so bear with me.
The freestanding roost is located in one of the short ends of the coop. I basically built a rectangular base with four pieces of lumber, then made two U-shaped roosts that I installed upside down to the base. I don't have a lot of construction skills, so I attached the uprights to the base with L-brackets. One is about six inches higher so the bantams and the full-sized girls could choose their comfort level.
The higher roost is still significantly lower than the hardware cloth covered ventilation "window."
A poop shelf currently still rests on top of a couple of concrete blocks but will be attached to the roost uprights with L-brackets someday (which is when many of my projects are scheduled for completion).
One advantage to the freestanding roosts is that the structure will be easy to remove in the spring when I have decided to make it a corner unit instead for easier access. Despite having nest boxes, my hens have decided they like to lay eggs directly under the poop shelf, apparently so they can watch me struggle to reach their little prizes. If I angle the roosts into the corner, I shouldn't have to lean onto the often-poopy roosts to get to the eggs.
Hope this at least gave you an idea. Good luck with your build!
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