Regarding the marquee tool, you have the option to use it and show either the elements on the current floor or the elements of all floors.
From what you are saying I understand that you are working with the first option and want to use the second option.
In you plan view with the marquee tool selected look at the floating window that shows construction ways (mine is at bottom of your screen). It is the same palette that you use to declare if a wall is straight or round.
There you will find a button that shows the marquee either bold or not. The bold marquee is what you are after. Use the F5 to refresh you view.(?)