The initial floorplan is where you begin to turn an old structure into the building of your dreams. Working in 2D is the easiest way to sandbox your ideas and see how they might work. Test actual space available, check your flow, see what you have room for and where. Changing your mind in 2D costs nothing and can crack wide open the imagination. By the time you hand this over to the builders, there can be no mistake as to what you want, where you want it.