Hmm, let me calculate.I suspect a lot have got more used it during the lockdown!
I am more worried about your roof now than I was before, if a chicken running across it sounds like a large animal from below! How thick is that ply? and how much soil under the grass? ('not enough' is the answer, methinx ) Or is Able a particularly chunky chicken?
There's the ply that 1" marine ply. A coat of water proofing paint. Then the butile sheeting which is 1.5 mm thick. Then there's 80 mm of insulating batts. Then there's the heavy duty poly sheeting. Got drainage board on top of that. The minimum amount of earth is 10".
Each square metre will take a 1700 kilo loading. The donkeys trot across it from time to time.
It's taken the weight of a 360 degree mini digger on boards.
Don't do chunky chickens here. they are all svelte and fit looking. You've been looking at too many BYC pictures.