Concrete Strength of Floor

Laingsburg,  U.S.A.

I am constructing a garage floor 7 foot below my original floor --my local building permit requires --how much weight will the upper floor support ?(Autos).

The floor is 21 x 25 foot concrete slab which is poured over a metal sheeting. this sheeting is placed across the 25 ft. span --overtop (3)  4 x 6 inch I-beams running the 21 ft. span, with an opening of 6 ft between each I beam... the concrete will be 4.5 inches thick with 1/4 inch re-bar in it.   I have a drawing of the idea if you need more info.  Please let me know as soon as possible-- so as I can get my permit approved and can get started on the construction.    Thank you!  
What you are asking is a structural design analysis.  By law I am forbidden to do that in a state where I am not licensed to practice.  Besides, an engineer will need more information regarding the footings, beams, additional loads, etc.  I  strongly recommend you consult a local structural engineer.  This type of analysis is straight forward.
Thanks Doc!

I was hoping to once again skirt the long arm of the building inspector-- but your right-- I need to do this right the FIRST time. Thanks for the speedy info! Gary