A skin-panel sub-frame panel having spaced, upper, lower and lateral edges, designed to occupy an upright plane adjacent the outside of a plural-story building frame, with a vertical dimension which is substantially the same as inter-floor story-height in the frame. The sub-frame includes (a) an elongate beam component defining the sub-frame's upper edge, and (b) plural interconnect-accommodating site structure sets formed in and distributed along the length of that component organized with (1) a first, upwardly facing set, and (2) a second inwardly facing set, which sets define orthogonally intersecting interconnect planes. Each first set accommodates a position-stabilizing, load-transferring inter-sub-frame interconnection between a pair of vertically next-adjacent sub-frames, and each second set accommodates a similar interconnection between a sub-frame and building infrastructure which is located within the mentioned building frame. Elongate lateral extension structures interconnect the panels with poured-in-place floor structure disposed within the associated building frame.