Prepare and roll out cookie dough. Cut with gingerbread house cookie cutter. Bake and cool cookies.
Use tip 4 and white royal icing to pipe peak of house and top of chimney; cover with rainbow nonpareils. Use tip 3 and red royal icing to outline door with zigzags. Use tip 3 and yellow royal icing to outline and fill in windows and windows on doors; let set. Use tip 3 and green royal icing to pipe dot doorknob and zigzags shutters on windows. Use tip 3 and red royal icing to pipe fleur de lis over windows. Use tip 4 and white royal icing to pipe icicles on windowsills.