Dip one edge of a front wall into the caramel glue until the edge is completely covered. Attach it to a side wall at a 90° angle and hold together for a few moments while the caramel glue hardens and sets. The caramel glue will dry very quickly. [Editor’s Note: The caramel glue is extremely hot. Assembly should be done by an adult only.]
Attach another wall and the back panel to the house so you have the base of the gingerbread house. Hold together for a few minutes while the caramel glue hardens and sets. Then use cans or jars to prop up and support the walls while they set. Let it set, undisturbed, for 30 minutes.
Remove the supports from the house and attach the roof panels. You will probably need to reheat the caramel glue to return it to a liquid state. Use a pastry brush to coat the edges of the roof panels and edges of the base of the house where you will stick them. As the angle is steep, you will need to hold these firmly with your hands for a few minutes while they begin to set. Then let it set, undisturbed, for 30 minutes.
If necessary, add a little water to the royal icing or add some confectioners sugar until you reach soft peak consistency. Spoon the royal icing into a piping bag fitted with a fine nozzle or spoon it into a large resealable plastic bag and use a scissors to snip off the very tip of one of the bottom corners. Only fill the bag halfway so you have room to twist the bag and gently put pressure on the icing to ensure it comes out in a smooth, steady amount. Decorate your house by piping outlines of windows and doors, and elaborate scalloped patterns on the roof. If you prefer a more rustic, snowy look, simply use a larger tip in your piping bag or snip a slightly larger hole in your plastic bag. If you miss any spots in your decorating, let the icing on the house set, and then go back and fill in missing spots. To attach candy to your gingerbread house, use a dot of royal icing to secure them and gently stick them to your house. It really is almost too good to eat!