Adding to design issues is the current fad of no eaves. What is saved in a bit of roofing and trusses is spent tenfold in higher wall maintenance (and possible water seepage)let alone higher lifetime cooling costs.
As for wet areas, I am currently doing my bathroom as an owner/builder and there is no way I would try to skimp on falls to the waste. No matter how difficult it is to lay the tiles I am only going to lay the tiles once! Water problems are forever(till you rip the whole lot out and do it again). That said, I am not working against the clock and can afford to piss around with things till they are right.
