Hello!  2nd post.  Thanks for reading.
Focusing in on the foundation for my barn/residence project.  Even grade property is a .25acre.  Black Mountain, NC, in-town, soil is normal, not rocky or water-saturated.  Frost line code probably requires around 18" deep pier holes.  Looking to seize on the most green solution on a tight budget.  Reclaimed materials for a pier foundation sounds like the obvious choice.  My project will be a barn, with the ability to drive through the middle.  Therefore, I only plan to have conditioned space one one or both sides of this feature.  No slap for the drive-thru as its energy intensive.  Thinking gravel of some kind.  Its where I want to be able to build tiny-houses, lawn furniture, whatever; protected from the elements and out of sight of pesky inspectors (property is located 2 doors from Town Hall). 

For now, as a building newbie, wondering what kind of reclaimed materials would do the job for a pier foundation.  If going with wood piers, would telephone poles meet code?  Would there be a way to treat the wood piers myself with 2nd-hand materials (leftover roof tar for example)?  The pier probably has to rest on a conrete form (in the hole), on top of gravel.  Reclaimed stone would work also though right?  How thick and what type of natural stone would be good for pier support?  Is the green benefit already achieved without worrying over this choice?  What about gravel?  Is river rock gravel more green than the granite-looking type? 

Thanks for your support!

I would investigate a shallow, frost protected slab on grade. No need to go below the frost line.

If its a drive thru, what are your wind conditions? Do you have a requirement to prevent uplift?