Use tip 3 and yellow icing to pipe in windows (smooth with finger dipped in cornstarch). Use tip 6 and white icing to outline and pipe in roof areas (smooth with finger dipped in cornstarch). Add jumbo rainbow nonpareils to back gabled roof.
Use tip 6 and white icing to pipe vertical line trims on house. Use tip 6 and white icing to pipe heavy outline at bottom edge of house; add mini multi-colored candies. Use tip 2 and white icing to pipe lattice design on roof. Use tip 2 and red icing to outline windows. Use tip 3 and white icing to pipe line on top of roof and add mini multi-colored candies. Cut green leaves to resemble evergreen branches and attach to sides of houses to form trees; attach with dots of tip 2 white icing. Use tip 3 and white icing to pipe icicles on windowsills.