Been there done that... Around here anyway, even a worn out one costs 1500 bucks. Conventionally building a comparable space (2x4/6 with roof and say t-111 siding) is way cheaper. And that’s all you are getting is a floor, 4 walls, and a roof, and that is assuming the container is still water-tight (a BIG assumption)
I’m curious as to what “wears out”.
Not a lot of moving parts, and this isn’t like auto sheet metal.
Your local hardware store sells roofing tar...that'll make any steel roof leak proof. And there some new silicon products that can be painted over...and are still cheap.