Yes to all. I have bought, borrowed, created my own, and downloaded drawings. As for making things on the fly, that is hard to answer as I can't recall making anything that I have not made, at least in part, before.
However, when I do find myself on unsteady ground, I make a model with playdough. Then I take that and transfer it to iron. I could take exact measurements, but for the kinds of things I make, that is seldom needed.