I'd like to do this on ours, except our front garden is at an angle to the house - I haven't measured it, but I'd say it slants at an angle of 25 degrees or so to the right as you stand looking at the house.
My question is: could we put an extension on like this but with one side angled and the other straight? It would mean the sink would have to be on an angled wall and the whole thing might have to be slightly wider. But I'd really like a downstairs loo. Would this look weird? Is it even feasible?