Start your project. Click the Pencil icon to the right of "Levels" to bring up the Levels dialog box. Input your levels and elevations as needed. Simply follow the requirements of the job is all.
Now on to creating your Constructs.
Create a construct for each workable floor. (In this example I renamed the first Level as "Datum". This is simply my preference, since most of the time I work on jobs with a +100'-0" as the First Floor or Ground Level. Copy my method, or use your own - either way, this level doesn't need a Construct since you won't be designing anything on this level) Remember to use the Division Checkbox to associate the Construct to the proper level. I keep it easy: Name "Floor 01" for both the Level and the Construct, and so forth for the rest. No need to complicate things.
After you get all your Constructs set up, now you can create Views. You can use Views however you like, whether it be to associate one floor in Plan View, or whither it be to associate all the floors to have a combined 3D View.
In this example I want to make a View of All Floors.
Right-click to Select All the Levels.
Include all the Constructs.
And now you have a "complete 3D Model".
If you open this up, you'll notice that everything is elevated +100'-0" since the Constructs are XREF'ed and inserted at their respective Level height you set up in the beginning of the job (of course, you'll be looking at blank Modelspace unless you start designing and putting some objects/models in each Construct).
When you work in each Construct, you are working in 0,0,0 space. The "View" is what brings it all together and places each Construct at the correct Z elevation. This way, all your Elevation Tags are represented from AFF instead of +124'-0" or whatever it may be due to the "sea level" you'll be working with.
It'll take some time getting used to, but when you do you'll never go back to the old way. This is similar to how Revit works, although Revit is still WAY better at things like this.
Hope this helps you some.