Abstract: A set of polygonal panels with novel interlocking flaps for the construction of various structures, such as buildings desk sets and the like. The panels are shown as rectangular and triangular, for illustration purposes, but may be of other polygonal shapes. Each panel has flaps along its sides, each flap having a wide central slot and two narrow adjoining side slots. When flaps of adjacent panels are placed in superimposed matching relationship, a pair of locking elements having radial grooves are introduced singly into the center slots and are separately moved into the side slots to firmly lock the adjacent panels by two locking elements, one in each of the side slots.