Since it's impossible to build a perfectly level floor, or flat roof, I design and build with a 1" over 8' slope (~ 1/100). Water then flows predictably, but 1/100 slope is sub-conscious. That cover's the issue when a pipe breaks or a large spill occurs, the flow is directed to drains in the floor near the wall edges , and away from the expensively carpeted areas. I know inundation it not supposed to happen but it likely will, hurricanes happen. Do normally minded architects consider that in building?
I'm setting my piers for my tiny 20x20 and I just surveyed the tops for that slope. TIA Ken