The IBEW building has exterior walls that look like they're built in sections that overlap. Because of that, I couldn't just put brick-imprinted fondant on in one layer and call it a day.
After giving it some thought, I decided to use chocolate and modelling chocolate to make the walls in separate pieces, then assemble them using the overlaps. The reason I decided to use chocolate is that I never trust gumpaste to dry hard enough to stand up and not soften up again (I'm paranoid.) The pieces needed to be able to stand up on their own since some of them would extend in front of the others.
sections on melted chocolate
I also wanted to make sure that if there was any breakage there would be some kind of a safety measure so that I wouldn't have to redo them at the last minute. With two layers of material they'd be less likely to break.
In addition to that, cakes that are totally covered with gumpaste just make me not want to eat them. Chocolate is another story.
cutting the pieces
I used cardboard templates cut to scale and cut out the sections of modelling chocolate, then imprinted them with the brick pattern using a clay texture mat.
After they were cut out I spread melted chocolate on a cookie sheet covered with parchment paper, then put the sections on top of the melted chocolate and let it set up to where it was almost cooled but still flexible enough to cut without cracking. I used a pizza cutter and trimmed the sides so that they were the right size, then let them set up some more until they were totally firm.
When the pieces were set, they were strong enough to pick up and move around without much worry of them breaking. The chocolate did crack when I was taking one section off of the paper, but the chocolate clay stayed attached, and I was able to repair the crack with more melted chocolate.
Once all the walls were ready I applied the windows and the upper part of the walls, which were white chocolate clay, using melted chocolate as glue. (Another good reason to use that method for the walls was that I could then use melted chocolate to assemble the entire building when the time came.)
Overlapping sections with trim attached
When the time came to assemble the walls, I covered the sides of the cake with fondant, then attached the walls with melted chocolate. I then attached the sections that overlapped, and covered the semas at the top with modelling chocolate "flashing" that mimicked the borders on the actual building.