Architects (I imagine) begin in much the same way as writers: a blank page. From there we differ largely, I think. An architect will sketch out a drawing, adding onto it rendering a complete outside shell. From there they move on to create he insides, rendering it into blueprints that takes into account all of the structure’s needs.
Writers—okay, I won’t generalize. I start with a blank page, but then I move onto a single idea. It’s usually a sentence. A question. Most of the time it begins with “what if. . . ?” That sentence becomes the heart of the entire book, spreading out from there, but it’s haphazard, a hairsbreadth away from random. I know about the long held debate about plotters vs. planners, but I think even the plotters have a haphazard growth to their books. It doesn’t take much for a character to end up derailing a plot, or for a scene to work in your brain but bomb on paper. We add on new growths to just stick on and hang off the novel. In no way is a novel a streamlined structure.
Architects have it pretty easy in that regard. No one would buy a novel if they could see a complete outline of how it looked on paper.