In many counties, a pole barn requires no permit. By code, they are generally intended for storage of animals or diesel-fueled agricultural implements, etc. Having said that, many people build them, pour a floor, and they become a shop. By typical definition, a pole barn does not have a foundation, but rather uses 4x4 or 6x6 poles buried 4-6' underground, spaced every 8'-12' or so, and then have supports and siding attached to them. There are dozens of pole barn building companies all over Colorado who could help answer your questions.
Steve H. - KE0KNH
Colo Springs, CO
'78 FJ40, '89 FJ62, '98 4Runner