I liked the balls of this one which was in the Guardian couple weeks back.
Matchbox house by Archmongers is a playful and functional rear outrigger.
Dormers are dormers tho really - people with money + design aspiration use zinc and glass. I'd be wary to use timber cladding up high.
It was pretty far past it, but house has been in the wifes family for 100 years, so sensible approach didn't come into it.