I've thought that would be cool as well. However (at least as far as indoor goes...) that's the way the floors are poured. While you could "frame" up a wood floor to have different elevations, I'm not sure it would be very cost effective, but it would be cool.
I've never raced on asphault, but I know a lot of parking lots are not flat and do have some elevation changes (usually for water drainage) , but most I would imagine are not sloped enough to matter.
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