Mix the dry ingredients. Whisk the flour, baking soda, ginger, cinnamon, cloves, and salt in a bowl.
Cream the butter and sugar. Beat the butter and brown sugar until combined. Add the egg and molasses and mix well.
Make the dough. Gradually add the dry ingredients. Mix until a firm dough forms. Add a little water only if necessary.
Chill the dough. Divide into discs, wrap, and refrigerate for 1 hour.
Cut the house pieces. Preheat the oven to 350°F (175°C). Roll the dough to about ¼ inch thick. Cut out the walls and roof using paper templates.
Bake. Bake for 12–20 minutes, depending on the size and thickness, until the pieces are firm. Trim the edges while warm if needed.
Cool completely. Transfer the panels to a flat surface and let them cool before assembling.
Prepare the icing. Beat the powdered sugar, meringue powder, and water until thick and stiff peaks form.
Assemble the house. Pipe icing along the edges and join the walls on a sturdy cake board. Support them until stable.
Attach the roof. Secure the roof panels with more icing. Let the house set for several hours or overnight.
Decorate. Add gumdrops, candy canes, chocolate candies, pretzels, and sprinkles using royal icing