Corrugated iron usually ends up a mixture of zinc coating and rust.
I wouldn't like to plunge headway into a fully rusted roof so I show my compromise.
Initially coated with a grey wash, the iron has been daubed with light brown,brown and green.
All this was then given a wash of Games Workshop Badab Black- wiped off with a piece of kitchen roll whilst still wet.
The green? Well, the left hand side is under a tree so a bit of moss has grown.
What do you think?