Abstract: Building constructs for constructing a play structure, a useful construction construct, or the like. In one embodiment, the building constructs are extruded cuboids having notches or other interlocking features. In another embodiment, the building constructs are encased within a polymer shell for enhanced durability or other desirable property. A play structure comprises a plurality of the building elements connected to one another. In one embodiment, the play structure comprises a cabin. Walls of the cabin are constructed by interlocking elongate wall elements. The cabin includes a roof constructed from interlocked flat panels or slats. A roof support elevates the roof over the walls and connects the roof to the walls. A method of constructing a play structure comprises assembling a plurality of the building elements.