Hi! I am pretty much a newbie, but we converted old greenhouse to a coop and put in the sand floor. We used kids playsand as it is washed and clean of clay and those things you would not want in kids playbox. It never clumps.
We laid down landscape cloth, the gray weed control cloth, under the sand, and on top of the brick greehouse/coop floor. We figured this had plenty of drainage, breathing, whatever.
But, this coop is next to a retaining wall, and the last rain, the sand got wet from the base of the retaining wall ground water.
SOOO, I would recommend placing the heavy duty visqueen plastic under the sand if you are on bricks or close to earth. I guess if you are up on wood coop floor it is not an issue.
My coop is 10x10 and I think we ended up with 7 bags total at about 5 bucks a bag. not bad since it takes little care, and is very easy.
Oh, I don't have a run because i let them out into yard in morning and back in coop at night.
If I did have a run, I would have the same visqueen, keep it dry concern. wet sand is cold. 1/2 of the coop sand got wet a few weeks ago and is still wet.
and they tend to say away, off of the wet sand. i don't see any foot prints there, which makes me think they don't like it wet.
If we miss a few days of coop clean up and it smells, the smell is instantly gone once we have raked and cleaned it up. pretty nice. we are composting the poop and sand rakings. don't know how that will turn out.
good luck!