I'll also throw in the fact that even for some reason you wanted metal, we've also solved the 'make a metal building wherever you want it' fairly well too. It is designed for adding doors, windows, comes in a kit form, and also breathes and can be insulated to have pleasant thermal properties. Even just in $/sqft having rechecked on this idea the price was never so much better than other kinds of buildings that are more suited to be in livable spaces.

Really what I would have wanted to see is people handling disposal of containers and then using the broken down materials to build a structure and/or just being smarter about reclaiming the material, but I haven't seen that come up in passively looking into it.