When you're adding a new slab, what often works best is to recess that area so that you could either make a curbless shower, or have a lower step up/down height.
There are a couple of ways to handle the waterproofing, but you do not really want to try to make your slope out of concrete. Your recess can have a flat bottom, but you'd then use a different mix to pack either the preslope or the setting bed, depending on the type of waterproofing you choose.
A traditional shower construction would have a liner installed on the preslope, you'd use curb corners to seal the cuts you must make for the top of the curb, and fold the corners around the rest of it. If your shower is larger than the size of the available waterproofing liner, you just bond them together.
If you want your entire shower to be waterproof, verses just the pan, then you'd use a surface applied waterproofing...generally, a membrane such as Kerdi or Hydroban (sheet, not liquid). Those require a special drain assembly, and you use the same material to waterproof the walls, so the entire enclosure is totally waterproof verses water resistant.
Check out
www.johnbridge.com for more specific help, and come back here for plumbing questions.
