It can be surprising how much fun kids AND adults have making their own gingerbread houses!
For our party, we don't use patterns but have molds we found a few years ago. I've seen them via mail-order and I think at Sur La Table too -- we picked up a couple originally, so we could bake 1 house at a time. They came with a recipe that doesn't make the most tasty gingerbread, but works for construction-grade.
Don't forget a supply of bases. Our cheap solution is to cut up some cardboard boxes and use those.
In order to have the pieces fit together decently, you oftentime needs to smooth the edges down so they're not as bumpy. We hand out butter knives and have our guests do this on their own pieces.
If you use pastry bags for the royal icing, just plan on nobody knowing how to use them.
Therefore, make sure you seal off the ends or you'll have a huge mess on your hands!
In addition to candies, don't forget that breakfast cereals make good decorations too. And if you want to spell things out and not do it in frosting, mini pasta letters work great.
Our party lasts about 4 hours, from the first guests arriving and being given gingerbread pieces to the creations getting judged. Your mileage may vary based on how much you prepare for your guests or let them do.
Adam