According to IBC2009 Section & Table 2308.9.1 Page 483. If using Utility Grade studs your wall can't be any taller than 10' & your studs (2x3's or 2x4's) must be no more than 16"oc.
WI's Uniform Dwelling Code (UDC) Page 43 & 44 Section & Table SPS 321.25.A doesn't have the IBC's utility stud stipulation. Therefore, 24"oc is fine if your wall is no more than 14' tall for 2x4's. But, with 2x3's you still must be 16"oc with a wall no taller than 10'.
However, if you're worried about being "legal", then you should apply for a permit to have your design approved & be wiling to conform to all other standards & inspections. Such as, GFCI protected electrical outlets every 6', air conditioned space similar to the rest of the house, insulation, ceiling & floor finishes & emergency egress. Basically, willing to make it truly habitable space, so they can bump up your taxes after they bled you dry with fees.