As Keith mentioned, you typically want to draw all walls at the floor (level) they are associated with. However, if you have situations like a foyer or family room that are open through the second floor, I would draw a 20' +/- wall (10' first floor wall + thickness of second floor floor system + 9' second floor wall) on the main floor. When creating the roof just make you select the "multiple floor roof" option to be able to reference a roof edge to a wall that's on the main floor plan if necessary. On the second floor plan you would still want to show a wall in plan view, but if you draw a 9' wall it will show 2 walls in 3d. So you could break the wall and uncheck "extract in model" in the "common" tab for that section of wall...or you could just draw lines for that area (I usually have a note stating "20'H 2x6 wall from below", or something to that effect). If you choose to draw the additional wall on the second floor, and you use softlist for estimating materials, you would want to exclude that wall. Seeing that you drew a 20' wall on the first floor the material would be figure properly.
Drawing all the walls first, then editing the heights is the most common practice, but if you wanted to take the time you could save new wall names if the wall definitions. For example: 2x6/siding/10'. Then when you start drawing you could choose that wall and not have to edit the height later.
I had made mention of this in another thread, however I don't think it's very common - I always have 2 instances of softplan running, and I copy & paste with the softplan clipboard from 1 instance to the other all the time. When starting a new drawing you can copy the entire floor plan from one project and paste it into another, then use "draw select" and select anything from the plan you just pasted to start drawing the new floor plan. This way you will be drawing the walls with the heights that have already been changed. You can select anything you want - windows, doors, symbols, notes, arrows, etc. without searching through menus or even using toolbars. I have found the combination of this, and using keyboard shortcuts makes for drawing a complete plan extremely fast. This can be done with projects that were created in earlier versions as well.