Hello, the program does not offer the option to create each level independently. When you create the building you have on the left hand pane the option to select which story to view, starting by Ground Level, 1st Story, 2nd Story, 3rd Story, Basement and Foundation. Simply click on the story you would like to see or work on so you can see it. If you have each story on different parts of the project grid then you won't be able to merge them together.