If it's for slum shacks then you are going to need to rough it up a lot more than that. Corrugated iron rusts pretty badly, and by the time it's thrown out and picked up off the rubbish heap by people to make a slum shack it's a bit bent, there can be holes in it, and it's usually pretty badly rusted. Google is pretty good for getting an idea of just how bad it can deteriate.Rusted metal
It's usually held in place with a large round headed type of roofing nail, and rust will form around the hole punched in the spot the nails are and can run down from there.
For slums, it's often only held in place by the weight of a worn out tire, brick, lump of broken wood or anything else with little to no value.
So it's a good start, and useful for fairly new dwellings, but if you want slums you want rust, wear, shabbiness and plenty of it.