KD,
Jthornton bought his fabric, so he knows exactly what his is, I'm sure he'll be along soon with a reply. The 24 inch box I got from Hengear.com uses what seems to me is a nice thick waterproof vinyl, with a white cloth embedded in the center. It has a sort of small pattern embedded in the surface of the fabric, you can see it in the attached photos.
Hengear recently switched from a V slit in the curtain, to a rectangular cut, and they say that works better, but I don't know the reason. On their's, the rectangle is five inches wide and has about 3/4 of an inch of fabric along the top. The curtain is 3/4 of an inch from touching at the bottom. I've seen two hens in my box several times, even three.
Personally, I'd just go with a single community box, with no individual boxes. I think that would just confuse them, plus it defeats the purpose of saving space and certainly you wouldn't want the bother of building three roll out boxes, and the advantages roll out offers, is too great to ignore in my book. There's simply no question Jthornton's box is plenty big for 15 hens, heck my smaller box would probably work.
View attachment 1246548
The box is 24 inches wide, 11.5 inches deep, and the opening in the fabric is 5 inches wide, the fabric is 3/4 of an inch short of the bottom.
View attachment 1246549
You can see the tiny pattern in the vinyl and the white fabric center to the fabric.