theres another thread going around about this subect. here's what I did.
I added the crushed limestone was because the rain would
cause my run to be a stinky swamp you could smell it 100 feet or more away, I had unhappy neighbors. so I added the 4 tons which made the limestone 4 inches deep, I left the area under the coop dirt thats where the ladies do their dust bathing and enjoy the shade on hot days.
I dont scoop poop anymore because when we have thunderstorms/rain or heavy rain like we did last night it washes all the dropping down the 4 inches and into the dirt it's almost like a filtering system plus the limestone is good for my girls they still peck and get bugs in and on the stone the funny thing I have noticed is black beetles crawling in and on the stone and the ladies love em
all I do is rake the stone out once or twice a month because my girls still like digging holes. I am 100% happy with the decision I made to cover the run in crushed lime stone. remember if you add it make sure its a minimum of 3 inches deep otherwise it wont do much good.also without rain the dropping that are on the stone dry up and don't smell.