We started with an 8x12 shed on cement slab. The shed is divided into two halves - theirs and mine where my side is storage for their feed, pine shavings, coop tools, etc.
The nesting boxes are 12" diameter PVC pipe. The roosts are cedar branches trimmed from trees on our property and are removable (sit in channel supports). The 2x4 on the floor holds back most of the pine shavings that fall from the roosts and also sits in a channel so it's removable.