If the work is being done as you've described....you are throwing $$$ down the drain again.
Why did you wait until work started before you became concerned? You still don't seen to know what or how the work will be done. You mentioned "dietra" (Ditra), I doubt the contractor will be using Ditra in the shower in any way. It also sounds like he is not doing a Kerdi shower either. Sounds like a standard shower job with several mistakes. Maybe the wrong tile setter?
Go here to see how a "standard" shower is built; http://www.ontariotile.com/preslope.html
Go to my photo albums to learn how a waterproof & watertight Kerdi shower is built; http://picasaweb.google.com/tile4youinc
For consulting about how showers are built have the contractor (or you) contact me.