Perception of slope is largely dependent on the context, as j indicates. From a physical perspective, it's hard for most people to realize they are walking on a slope, if there are no visual cues and it's a relatively short distance. (If no visual cues are present and no additional leg strain occurs, people are less likely to notice the slope)

likewise a flat floor might feel sloped.

for example, the gallery in the image below on the right is level, but the heavy presence of the angular structures in the wall compels one to feel as if walking on a slope. it can be quite unsettling if you focus too much on the visual cues from the structure. of course, if you stop looking at the walls and simply walk, it feels much more natural.

*anti-per bump*

When the Columbus Convention Center first opened, employees were often spotted putting balls on the floor to see which whay they would roll. The floors were perfectly flat. The context was what was screwy.

Silly Eisenman.

2.5% is pretty much the max. Even at 3%, most folks can tell that things are off because of the way their foot makes contact with the surface they're walking on.

Just to add:

You should test it out, if possible. Grab a sheet of plywood and do some mock-ups or grab a drainage plan for the campus and check it out.

in a small area, even small slopes can be easily detected by eye.

much more than of a slope than this and people might begin to notice.

I saw a project once, in school, that had a 1% slope that the designer treated as a flat surface. It allowed the building to climb one storey per revolution of a 'spiral' floor. Kind of a cool idea unless you're a bowler maybe.

Careful not to confuse 'flat' with 'level'. i.e. Most of the decks on a cruise ship are 'flat'. Passengers are fooled into thinking they are 'level' so much that when they get onto terra firma, it's the dockside that is listing !

No, that's a fIat.

The ADA and ANSI would require maximum 2% slope in door maneuvering clearances, accessible parking stalls and other spaces, a path can have up to 5% slope before it requires handrails. The people who will be most sensitive to slopes on a floor are the folks pushing or pulling carts or wheel chairs. Taking a cart loaded down with a bunch of books down a hallway or around a room can be quite revealing when the floors actually slope or have difficult surfaces to roll over.

Over and OUT

Peter N