Don't quit your day job over it. Sooooo many people build there own racks/cages and then also build them for their friends and/or local breeders that there is not that big of a demand IMO.
If you are set on moving forward with it:
I would look into XPVC and build the racks/cages out of it. It is more expensive then melamine but it is much lighter and very easy to work with. Look up C Serpents Racks
Plus the XPVC should help on your shipping costs when you do plan to ship.