Thanks for your advice. I can stop the check, but I don't think I will get much from the contractor, he is an independent contractor that a friend recommended.
The pitch is from the back corner, sloping acoss the back, and towards the front, water will collect in the opposite corner. The slab does have channels, two runnig front to back and two more across the width.
Other then tearing it out, could I have the concrete ground down?