One traditional way to do design is by making a decision tree. Do you have a human being selling tickets, or do you have an automated machine? How do you delimit the queue of people – is it free-form or does it have some physical barriers? What is the shape of the booth or of the machine, based on where you will put it? Indoors or outdoors?
With this method, you run into combinatorial explosion pretty fast, especially since you must consider every decision against every other one. And *still*, realities will emerge from the system, and you need to let it find a stable configuration by itself.