To save your floorplanned design, select File 
Save.
The Save command creates a file with the same name as the current design and the extension .fnf. The information stored in this file includes the design's hierarchy organization; floorplanned logic; and net, logic, and color assignments.
This file represents a snapshot of the current state of the floorplan that you can use later.
In addition, whenever the FNF file is saved, the floorplanner automatically creates an MFP file. The MFP file contains all the physical constraints for the design that appear in the Floorplan window, and is used as an input to MAP.
