I create molds. I design in CAD and create mold masters from HDU foam on the CNC. From there I create molds with urethane rubber or silicone. I don't use wheels but rather a swivel plate bearing and a bottom disc. Wheels don't work well on anything but a smooth surface, and even then they tend to wander. This works anywhere. The next designs incorporate epoxy resin with cement and those masters will need to be 3d printed. I only have a basic 3-Axis CNC and it isn't up to creating the designs I want.
As for mix...I have tried and tried to find an alternative to the expensive stuff I use to no avail. I stay with Rapidset Cement-All and add polymers and glass fiber for strength. I have tried a lot of alternatives and never come close to the strength and rapid curing of Cement-All products.
This is a pic of bottom disc and bearing. I have a few different bottom discs but same idea for all.