not sure if you have already considered this, but the outside design of this building will be almost equally as important as the inside. My suggestions for the outside area are listed below:
~ Rotating Burger like-sphere on the roof.
~ Large Billboard advertising the fast food restaurant
~ Large dramatic lettering positioned on the front face of the building, possible flashing.

Some of those may sound obvious, but would be necessary to give the restaurant a bold iconic look. If these graphics are used and polished they will most definitely give the 'chique' look