A method for constructing three-dimensional structures with a multi-part construction toy comprised of connectable component parts. A flat construction plan is provided illustrating in full size a two-dimensional structure constituting all or a large part of the intended three-dimensional structure. The connectable component parts are placed directly over their respective illustrations on the flat plan, and joined to form the two-dimensional structure. The two-dimensional structure may include a pair of opposite side subassemblies joined by one or more reorientable bridging elements, for example a flexible panel. After completion, the two-dimensional structure is picked up and erected to three-dimensional form by bending or pivoting the bridging element to position the opposite side subassemblies in spaced apart, usually parallel relation. The free ends of the subassemblies are then joined, usually by a bridging element, which may form an end element of the two-dimensional structure. Where desired, additional bridging components can be added to rigidify and embellish the initially formed three-dimensional structure.