Roll fondant 1/8 in. thick on surface lightly dusted with cornstarch. To ensure that panels line up at bottom, make 3 panels at a time; cut a piece 3 1/2 in. high x 14 in. wide for 9 in. cake, cut a piece 3 1/2 in. high x 15 1/2 in. wide for 15 in. cake.