My two desired modulars would be:
1. Carwash. I would love a modular carwash that would be a corner modular. The car could enter one side and be on a curved track to exit the opposite corner. The top level could be an apartment, or some kind of office. This style can be more similar to the Downtown Diner with neon signs and typical American retro style.
2. An business office building. Have a lobby room and mailroom on the first floor. The second floor can have cubicles and perhaps a break-room for employees. Finally a third floor could have the CEO's office with a balcony. I would prefer this building be in the style of 1950's New York type of building.