Teacher Process
The students should be given at least 3 full class periods and/or a week of scheduled out-of-class group time in order to complete this task. The roles are require a general group consensus on theme, as well as some complex design and number-crunching. Do not rush the students, and if it appears that the group need extra time, allow so. The point of this group is really the synergy of ideas, as, as one of the final steps, a rushed group might skip over this step and just throw the project together.
Simply provide the students with the task of creating a restaurant, let them choose or assign them groups of four students, and let them get to work.