There have been many discussions about metal roofing on this site. I thought I’d add a few comments from a recent experience.
I just tore down a shed/garage structure that had corrugated metal roofing and siding on it. The structure was one of those impossible to date scrap wood on dirt DIY buildings. I think the metal siding was added maybe 25-35 years ago to hold it together, but I can’t be sure.
The first thing I’ll say about metal siding is you get a lot of respect for it when you try to take it apart. If this had been wood sheathing it would have been down in half the time.
The material on there was the typical galvanized stuff you would find on and industrial or farm building. Probably the lowest quality, but given how well it held up, it says a lot about what to expect from a high quality product.
Before tearing it down, I was always a bit curious as to why only certain sheets had rust on them. These sheets were not in contact with anything different than the others. They had the same exposure to the elements. While demolishing the structure, I noticed the DIY genius had used aluminium roofing nails in some spots on these sheets (there were at least 30 different types of presumably recycled nails used). I assume electrolysis would explain the rusted sheets. Good tip to anyone planning to use this stuff; pick the right fasteners.
And now a special request. If anybody out there is planning to use corrugated metal on a structure, please make sure the structure is sound enough to outlast the projected lifespan of the metal. Think about the poor sod who will have to take it down some day!