I would first get some more information. Design a beverage machine application is vague. Is this a liquid beverage dispenser (Soda, Coffee fountain), or does it dispense bottles or cans of beverages (Coke or Pepsi vending machine). Is it coin operated? Is it for public use or private? How many different beverages does it support, (one or more)? Given that I understand the customer request fully I can begin to design the application. Once understood I would begin defining the atomic actions needed to deliver a beverage in this machine. (pull tap or insert coin, pick a brand or flavor, etc.) Once all the actions are defined on how someone would get their beverage I would arrange those actions into logical buckets and define how they interact. I would go over the flow and add safeguards, limits, and exception handlers. At this point I have a product that defines the "happy path" and has some safeguards to insure it works in a preferred environment. Now I can add bells and whistles to differentiate my product from the marketplace.