I know there is a bit of a debate over making royal icing with raw eggs or not with eggs. But when you are talking about a 3 foot tall gingerbread house you need it to stick together. What a lot of websites recommend when working with raw eggs is to make sure that you use properly refrigerated, clean, grade A or AA eggs with intact shells and to avoid contact between all of the bits, so the yolk, egg whites and the shell. It tasted great and no salmonella when we made it, however do note that it is a risk.
To make the royal icing: whip confectioners sugar and egg whites together until you get a nice even consistency. Here is my trick in order to hide my icing. I tint it the same colour as the gingerbread. I add a brown food colouring to my icing, so that it looks very similar and doesn’t stand out. My technique is also helpful for hiding the icing, I try to put it on as clean as possible, so the mess and the bulk of the icing is on the inside of the piece I am working on.