I guess if it's sloped even a little it's good enough for the most part?

Cool. Thank you for clarifying. I always thought they were level

If they are level and there's a hole (drain) in one side.... Would it not drain? If it's sloped you would require more drains. As an example, if the corner that op is expressing concern about is sloped where that corner being the highest point, you would need a drain somewhere on the opposite side of that slope. If it's all level then water would drain in just one drain eliminating the need to drain more things away from the house. The only problem with this is if you have a very large roof and everything is coming out that one drain it could overflow. Still at that point everything should be level without slopes with additional drains.

Are gutters installed on slopes? I thought they were level and just emptied on certain corners.

Wish I knew how to pin this to top