As one you recently spent around 12 hours (following a failed digital initiative) churning out a respectable tabletop game using nothing more than paper (& MS word ) & whatever bits I had in my bits case (I'm a little serious - but symbolic standins work at this level), I can tell you that you don't need TGC for the first prototypes. :c)
Tinkercad looks interesting. Thanks for sharing. :c)