A rotor blade section and a method for assembling a rotor blade for a wind turbine are disclosed. The rotor blade section includes a plurality of ribs each extending in a generally chord-wise direction. Each of the plurality of ribs includes an outer surface. The outer surface has a generally aerodynamic contour. The rotor blade section further includes at least one cross-member extending between adjacent ribs of the plurality of ribs, and an outer body mounted to the plurality of ribs. The outer body has an aerodynamic contour generally corresponding to the aerodynamic contour of the plurality of ribs.