It sounds like a combination of the following may be the best bet as a coop/run floor?
1. Pond liner to cover grass once chickens have eaten it all
2. Course concrete gravel (maybe 2 inches deep)
3. Sand on top of gravel (maybe 4 inches deep)
Can anyone comment on this if you have layered or combined gravel with sand, or laid sand on top of gravel. Good idea, or no?
Where are you located? Type of soil, and is the run dry or does it hold water from rain for any length of time?
Don’t think you woul need the layer of plastic.
If a wetter run, I have known people to use gravel/sand -applied when ground was dry. Then use hay/straw/clippings on top for chicken enjoyment.
However, chickens do like to scratch and dust bathe, so if you follow the gravel route, you should plan for a chicken dust bath area in the run. Dustbath:a mix of dirt/sand/wood ash/DE, small and fine grit (chick grit) in any combination but go easy on the DE.