[Either to use a whole lot of it, or to build a structure using other materials and cover it with a layer of oil-based clay.]
[Why not? If you're talking about oil-based clay in general, not a particular brand, then what other non water-based clay is there? What are you trying to end up with? If you intend to ultimately cast this in another material, you might be able to work directly in the other material and skip the clay step entirely. I have a recipe for oil-based clay posted on my site, under Techniques of Sculpture/Modeling.]
Andrew Werby
UNITED ARTWORKS- Sculpture, Jewelry, and other art stuff
http://unitedartworks.com New- Artworks Computer Tools for 3d Design and Realization