I have a job where a small former outside toilet is being converted into a hobby pottery complete with water supply and small kiln.
I propose to fit a small plastic consumer unit with the appropriate IP rating for protection against ingress of water.
This will be a home brew job with a generic enclosure and a RCD main switch and mcbs from my spares stock.
I have seen many metal enclosures rusting quietly away in detached garages/w/shops/outbuildings and thought they would be better served by using plastic.
I think there is still a case to be made for fitting plastic consumer unit enclosures in outbuildings in order to prevent deteriation caused by external influences. Moist atmosphere, unheated spaces and the like.