22 Jul 09 13:10
From someone who has participated in the construction of many parking structures and water treatment facilities ...
Floor slopes for areas that will see vehicular traffic, particularly in areas using chlorides in the winter, should slope at least 1/8" per foot - 1/4" per foot is preferable. 1/4" per foot is becoming more common as it drains water faster and helps to reduce penetration by chlorides into the slab. If this were an elevated slab, I would advocate for a level soffit (bottom) first, and a one-way bottom slope second. For a slab on grade it all depends on the contractor's ability to accurately trim the base material. Certainly you can save a bit of concrete by maintaining a constant slab thickness.
For your "train" - gnuguy
is correct about the cost associated with installing fill concrete or grout to provide the slopes, BUT
he has not considered the additional cost to construct the walls. Setting today's large form panels would require considerable built-in-place wall forms to provide a "starter" form that is level to set the wall form panels on. Setting these forms directly on a sloped slab surface simply does not work.