Shelving under roosting bars

[Ted Brown]

You could simply frame the underside of the shelf with two 2x4s that span end to end front and back. Will add weight; @Mother of Chaos' suggestion of trays would avoid having to move them.

 

[DobieLover]

Wow, that's beautiful! If I were a chicken in this coop, I would go outside rather than poop in this nice clean coop! Wish now I had painted mine. And love the butterfly!

That was before the dusty chickens moved in. And the spiders started decorating. It is nowhere near that clean anymore! But the pictures show the construction and necessary support for the boards.

 

[perkolator]

I would brace the shelves to prevent sagging, probably 1x2 lumber on the perimeter in the tall direction to save on weight vs thicker lumber that will weigh even more. I'd also use the trays on shelf as suggested, instead of moving the whole shelf every time.