The "correct" or ACA way to add a second floor involves using the Project Navigator, which is ACA's file management system. The first step is to create a new Project. The Project Navigator palette contains 4 tabs: Project, Constructs, Views and Sheets. The Project tab is your manager, and where you define your levels. Your drawings are all contained in the Constructs, Views and Sheets tabs. If your drawing contains 3 floors, you will have a minimum of 4 levels--one construct drawing for each floor plus your roof. In the Levels section of the Project Navigator, you enter the floor elevation and the floor-to -floor height of each level in your project.
The User Guide (the 4,000 plus page one) does have a thorough explanation of the Project Navigator, and Paul Aubin's Mastering ACA series contains a great overview (I have the 2010 book--I don't know what the latest one is).
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