On the old home place where I was raised there is a small building---a root 'celler'---built by my grandfather in the 1920s. It's still standing with its original corrugated tin roof. Yeah, it's rusty now, and probably leaking, but it's still there. In the surrounding area I can point to several old barns, sheds and even houses that were built as far back as the turn of the century with their original tin roofs. I've often thought that if that tin could have been turned over after about 50 years it would last a century.
When my parents moved from the home place I salvaged a lot of tin from my dad's garage/tractor shed/workshop that he built in the early 50s. That tin is now covering my tractor/tool shed.