I asked him the typical wall thickness, once I got a reply I told Mike the internal dimensions and the wall thicknesses (one wall was thinner then other three).
I am not sure if the wall height can be changed (well I am sure it can be made lower, but I think Mike would need to buy thicker material to make taller walls.
Also, you could probably adjust the base thickness (which would inversely effect the interior wall height).

Mike was very helpful and flexible. He did recomend if I wanted anything complex to Use CAD (I sent him an approximate scale image I made in Microsoft Publisher).
Once I finished installation (need to trim some screws) I will post a pic. I think they look 1000% better then the home made trays I had in there before.