A. Rocky Geans, president of L.L. Geans Construction Co. in South Bend, Ind., and member of the board of directors for the American Society of Concrete Contractors, responds: A garage floor does require a slope for drainage so water won't pool on the floor, and 1/4 inch in a foot is typical. But if you do a good tight screed and finish job, 3/16 inch per foot will do. And yes, the gravel sub-base should be graded to the same slope as you intend for the slab surface.
The bigger question is, where do you drain the water to? If you are located in a freeze-thaw climate such as we have here in South Bend, drainage toward the overhead door could be a problem.
to read the full article.