If you are developing a "Mall Tycoon styled" game, the GUI is usually custom-built rather than using a standard tycoon kit. Expert developers recommend:
For a look at how these Set Pieces and their corresponding GUIs function during end-game play, check out this completion walkthrough: Mall Tycoon GUI
Set Pieces are unique structures located at the end of every floor. They are more expensive than regular stores (usually costing 30% more) but provide significant income through "Mega Tips". If you are developing a "Mall Tycoon styled"
You must buy every standard upgrade and choose every store on a floor before the Set Piece GUI becomes available. Mall Tycoon GUI