Sorry about sideways pics!
Step 1: Getting everything ready
The hardest part was at the beginning, getting all the architectural units to hold together with the royal frosting. They needed to sit for a little while - not very long, but still a little while - with support so that they would dry in the right position and be stable. I ended up doing a frantic search around my house for understructure bits that were the right size. Things like spools of thread, marshmallows and small boxes just to hold things in place for a few minutes. It worked out alright, but I swiftly got off to a messier start than I had anticipated.