Sometimes it seems that there are a zillion different metaphors for how writers construct a plot. There’s the sculpture metaphor (carve away everything that doesn’t look like an elephant). There’s the pottery-making metaphor (add a lump of clay, work it until you have the center, then shape and add more clay as and where needed). There’s the jewelry metaphor (like stringing different colored beads in a pleasing pattern) and the quilt-making metaphor (combining small scraps of different-colored cloth to make a large pattern). There’s the soup-making metaphor (see what you have in the fridge and start popping things in a pot to cook; season to taste).
The metaphor that I’ve run into most often – and the one that’s been most descriptive of the way I usually work – is the jigsaw puzzle metaphor.