Aaaahhh, walls - what a luxury!
We have chosen an exterior ply cladding called 'Shadowclad'. It comes in large sheets and is 12mm thick with vertical grooves. We love it. Originally we were going to clear coat it to give a nice timber finish but advice from the manufacturer's suggested that the board would only last about 15 years if we did this, whereas they estimated a life of 50 years for painted boards. So paint it is. The colour is Wattyl 'weekender' and is probably a bit darker than it appears in the photo. We have found shadowclad relatively easy to put up - as long as the first board is true, the rest just slot into place alongside it.