Second hand corrugated iron is very cheap and plentiful around here- just about every building is made out of it.
You don't seem to use it so much in the US perhaps because of your cold winters?
I had a new roof put on my house a couple of months ago, so I had a whole house roof load of tin to build chook houses out of.
i was given a large pile of the stuff for free (over a ton)
so far i have put it on 2 of my coops & my woodshed
it had already been used a couple of times but it was very heavy gauge
probably dating back to WW2
the flock didn't say they cared about it being old & i'm sure they enjoy being kept dry all winter
i put mine down with screws so the wind can't remove it.