I built one on a previous project that was 9m x6m- configured broadly as a nice double with a single on the end (sideways if you get me)- that was the workshop bit ,with ample storage upstairs, albeit with reduced headroom. It was cavity wall, facing brick outer skin and concrete block inner.
Design and construction limited by planning regs in a national park area,my current one is as you’re suggesting- dwarf wall with timber frame and cladding under a slate roof- stays nice and dry and is quite warm too. It’s a double length with L shaped workshop that I’ve adapted to, probably not as useable as the one previously described.