You assemble a siege engine, using up to one fewer worker per two caster levels you possess. You can do without one additional worker if you have any ranks in Knowledge (engineering), plus one additional worker per 5 ranks you have in that skill. If your caster level combined with Knowledge (engineering) fails to eliminate the need for workers, this spell fails.
Section 15: Copyright Notice - Pathfinder Roleplaying Game Ultimate Combat
Pathfinder Roleplaying Game Ultimate Combat. © 2011, Paizo Publishing, LLC; Authors: Jason Bulmahn, Tim Hitchcock, Colin McComb, Rob McCreary, Jason Nelson, Stephen Radney-MacFarland, Sean K Reynolds, Owen K.C. Stephens, and Russ Taylor.