Galvanised steel sheet cabin sides rivetted to steel frames, and a wooden roof structure is a very strange arrangement. For a 1972 steel hull I would expect either an all timber or grp cabin. Sounds like this could be a one-off construction - perhaps an owner DIY build. I think the Rugby Boatbuilders connection is a red herring.

I think the AI reply that you received may have confused you. I don't know where it has found the information about Rugby being the only boatbuilder to use galvanised steel but I suspect it is incorrect. The one thing that we can be certain about is that in the 1970's, virtually all, if not all, Rugby Boatbuilders boats were made with their distinctive hull design - as per this photo : The cabins also had two other distinctive features - a very narrow (almost non-existent) gunwale, and louvre windows with curved corners that virtually nobody else used at the time. You will also see from this advert that they started building boats with steel cabins in 1977 (previously the cabins were wooden). The cabin on your boat could have been changed over the years, but if the hull isn't of this shape it's unlikely that it is a boat built by Rugby Boatbuilders in the 1970's.