A Wet workshop is a proposed space station constructed in orbit from a spent rocket stage.
Wet workshop studies
A wet workshop design was considered for the Skylab space station. A single S-IVB stage from a Saturn Ib rocket was to be used. However, when surplus Saturn V rockets became available after the Moon landings, an S-IVB was outfitted as a space station on the ground, and flown to space atop a Saturn INT-20 (basically a Saturn-V without a third stage.). During the space shuttle program, the huge external fuel tank was considered to be outfitted as a space station but various problems and safety enforcements due the the Challenger disaster made this impossible.
Problems and solutions to the wet workshop concept.
The major problem with wet workshop concepts is outfitting the fuel tanks in orbit. However, if the tanks were to be outfitted on the lunar surface it would make it much easier. Due to the fact that the Moon has negligible atmosphere, lunar landers need rocket engines to slow their decent. The decent stages of lunar landers, or cargo landers would be outfitted on the lunar surface, and covered with regolith. The overall volume would be much greater then would be needed for accommodation of the residents alone, but the tanks could, for example, be used as greenhouses. The tanks could also be used to store oxygen derived from regolith, or be melted down for scrap. Already refined metal and plastics on the surface would be much easier to process than lunar regolith.
This article reflects the personal opinion of T.Neo