Buy twice the candy and make twice as much frosting, cause it seems to disappear during the activity.
We did this activity in 2009 because we had a bunch of leftover ginger bread houses from Christmas. I suggest using these instead of the graham cracker houses you see in the pics. The premade houses look better, and are structurally more sound. They also make great group projects. Try to find them on clearance after the holiday season to save money. Participants can do them individually if you use graham crackers.
To save money, we make our own frosting. Add whatever color you want….
1 cup shortening
2 teaspoons vanilla
4 cups powdered sugar (sifted)
4 tablespoons milk
Buy a large pack of pastry bags. Load them full of frosting the day of or even days in advance. Then just snip the tip off when ready to use. If you keep the tip small, the frosting will go a long way.
If using graham crackers, I recommend constructing the house with hot glue. When you have a lot of people in the activity room and hands on the pastry bag, the frosting tends to get hot and structures start to fall apart when the weight of candy and frosting are placed on them.