The top mistakes people tend to make with gingerbread houses are often related to using dough that is too soft or rushing the assembly because they are excited! A lot of times, people will use a standard gingerbread dough recipe meant for eating. These recipes are often not ideal for building because they have higher moisture content and are thus less supportive. To avoid this issue, use a "construction gingerbread recipe" which is a recipe with less butter and more flour to make it drier and more firm. Another common mistake people make is not letting the gingerbread set or fully harden before assembling and decorating. Starting to assemble or decorate too soon after the gingerbread has come out of the oven will lead to the panels collapsing under the weight of the structure and decorations. Be sure to let the pieces sit out overnight to fully harden and set before assembling. Resist your excitement, and it will lead to a much more successful gingerbread house!
I personally didn't learn about gingerbread houses until I moved to the US and saw firsthand how kids and their parents would shop for gingerbread house kits once the holiday season arrived. I was so curious about its process that I attended a gingerbread-house baking workshop, and noticed how one mistake beginners (like me) usually make was assembling the house before decorating it. I find it's still doable to decorate once it's built but icing it when it's flat on a surface just gives me more creative freedom and even reduces the likelihood my design will be ruined if the gingerbread collapses due to weak "glue" used from the kit. This rarely happens to me, but when it does, my go-to solution is to make my own adhesive by melting sugar in a pot until it gets dark brown. I then carefully dip the edge of each decorated wall, which makes them stick better together; resulting in a more stable gingerbread house.
Gingerbread houses always test my patience. When I travel for work at Advanced Professional Accounting Services I sometimes try making one in a hotel room kitchen and funny thing is the icing always melts if the cookies are still warm. It felt odd at first to wait longer, like excitement were stronger than logic. I didnt rush the cooling next time. A litle thicker icing as glue keeps the walls steady and later it holds shape instead of sliding apart. I learned to keep decorations light until the base feels strong. Small fixes make the whole thing stand proud like it should.