When is a paper model not a paper model?

Givens:

1. I am new to this forum.
2. I could't find a discussion of this elsewhere in the forum
3. My forum searching mojo is not good.
4. I know that I should make whatever makes me feel good regardless of material,

But...
When is a paper model not a paper model? For instance, tape or plastic for canopy? Balsa wood for masts? Twine for rigging? Metal axles? What mixed media are acceptable (if any)?

Is this even an issue?
I don't want to spend hours on a model just to discover I am doing it "wrong". Or at least I want to know I am doing it "wrong" for the right purpose.

Thanks ahead of time.