My first coop/greenhouse had 1/2" mesh down low,and a mixture of chainlink and wire mesh fencing(2"x4" openings) up top.
I'm trying to exclude paws from grabbing my chickens with the 1/2" openings, and I use fencing with larger openings where that can't happen.
I think I'll be going with half inch mesh all over,since I'm out of metal fencing,and I'll need to buy more.
It's not much more expensive than chicken wire,so we shall see.
If protecting the birds were not an issue, I would use fiber reinforced plastic,snow fencing or
deer fencing to prevent water from pooling on the plastic.