The base material thickness, prep, and compostition are CRITICAL
to a good slab. It will depend a lot on your soil and frost
condtions but the amount you need will scare you. My clay soil
and 4' of frost needs 12" for a small slab and 24" for a larger
one. And it needs to be compacted down in layers using a vibrator
packer.

Be sure they use a 4mil (or more) plastic sheet under the
concrete to help control the moisture migration.

Bob Thomasson wrote:
The plans call for control joints every 12 feet but the concrete guy
suggested going to joints every 10 feet. They are going to be sawcut
to a depth of about three inches. The slab and footing will be poured
in one flat monolithic pour. The concrete guy also suggested using
wire mesh reinforcing in the floor in addition to the fiber additive.

The most important part seems to be to get a good compacted base that
won't settle or expand with moisture to place the concrete on.

Thanks for your comments.

Bob