In London I worked for a company which also made prefabricated units for construction, but not from containers. Construction time costs money, and in London it was crazy: landowners calculated every week of construction time as one week of lost rent, which of course could be thousands of dollars.

As you probably know, building toilets by the conventional method, on site, is very time consuming, so my boss had a clever idea. He approached the owners of a failing railway-carriage company who had a production line standing idle, and then got a contract to supply pre-fabricated toilets for offices. With a number of adaptations, he got the carriage fabricators to build toilet units for a high-rise office block. They were repeat modules with about 6 toilets/ basins to each room. From the outside, they didn't look much: metal strutting and exposed plaster board, but when finished, they were craned into place inside bare rooms on site, and were totally convincing. They had top-quality finishes and because of the controlled construction in the factory, the level of precision detailing was more like a car than a building. Rather cleverly, the ugly outsides of the modules were now hidden by blockwork walls, or formed part of the duct space, where all the services pipes were connected up.
The big win, though, was that the toilet-construction time was running simultaneously with the general building time: no need to wait for one trade to finish before the next trade went in. The owners got their building open quicker, which made them a stack of extra rent money.

And what was I doing? Working out and drawing up the details. My most worrying moment? For one job we were making some toilet cubicles of solid marble: divisions, plinths, front panels etc which were very precisely dimensioned. We also had permission to use a limited resource controlled by the Italian government: marble from Italy, from the same quarry that Michaelangelo had used. About 150 panels were cut, then put on a special train to England, so no room for error. As they were all cut according to my dimensions, I had a few worrying moments of doubt, I can tell you!