Using surplus shipping containers sounds like a great idea until you get into the details. The lumber they show in the video is needed to frame out the inside to hold plumbing, electrical, and insulation. Insulation is also needed on the floor & ceiling. Then you need drywall to cover. All of this reduces the usable space.

So all the shipping container gives you is an outer skin which will need paint to prevent rust. I don’t believe anyone has been able to make this approach cost effective. I can only hope someone figures this out some day.