Red plastic bricks with raised corners which interlock with underside of bricks in the row above. Bricks come in half, 1, 2, 3 and 4 unit sizes along with gable pieces. There are also blue roof tiles (including one modified to take a chimney) and ridge pieces. The tiles attach to the next row by sliding into an L bracket on underside of tile above. Cream windows and doors complete the set. Sets are accompanied by a delightful illustrated story booklet entitled "Periwinkle builds a house".