Note that the "CAD software guy" you mention is most probably an industrial designer.

They may spend most of their time drawing with pen and paper to give you a number of alternatives. Then you discuss the alternatives and possibly changes. After a while, they switch to 3D software to model the product, so you can look at it from different directions and in different lighting conditions. When you like what you see, they then continue by producing blue prints with required measurements to allow the construction of the tools needed to produce the case. You normally let the factory handle the construction of the tools. The tools don't just affect the shape of the box, but also the surface finish of the plastic. Shiny is nice, but you will immediately see scratches.