I don't have an exact scale in mind, however, I have access to some display models that I could copy. My particular subject is the Oribital Boost Vehicle (OBV). I live in central Alaska, so just running over to the local hooby shop or even a hardware store is not exactly possible. PVC pipe had not quite come to mind and I'll have to give that a try! Plus, I think it would even be capable to be put on a lathe and tunred down for the different sections, if the material is thick enough.
Thanks for all of the input!