If your plan contains different floor or ceiling heights and you want to include Ceiling Joists or Floor Joists then you need to understand how to use Levels.
A Level controls two different aspects for Joists. It controls the Height of the Joist and the Elevation (Offset) of the Joist.
The default Height for Floor Joists will be the height defined in Drawing Options-->Drawing Options-->Material Dimensions-->Floor System Options.
The default Height for Ceiling Joist will be the height defined in Drawing Options-->Drawing Options-->Material Dimensions-->Ceiling Options.
When you draw a Joist or Joist Set it is automatically assigned to Level 1 and given the default height. If you were to edit a joist in Level 1 and change the height or offset you change the height and offset of all other joists that belong to that same Level.
As an example let's assume that you have a floor system that has a portion that is raised up 1' above the rest of the floor. To achieve this difference in floor heights you would need to edit the raised section and assign it a new Level number. So in this case I would assign the raised floor section the Level number 2 and then change the offset to 12" Up.
If you have another section of floor that is also raised up 12" you can simply change that section's Level to Level 2 and that section of floor will take on the Level 2 properties. If you edit any of the joists that belong to Level 2 and change the joist height or offset then all joists in Level 2 receive that same change.
If you go to Options-->Visible Items and check Show Joist Level, down at the bottom of the dialog, then the different Levels will each have their own color. This aids in determining which joist sets belong to each level.
When working with Floor Joists it isn't too difficult to keep track of the Levels because typically all the joists will be the same height. The only variable will be the offset.
But when you are working with Ceiling Joists you may end up throwing another variable into the mix if you are setting up your joists to be the correct heights based on the Span Tables. Different Spans require different joist sizes depending on local codes, materials used, live and dead load requirements, etc. So even if all your Ceiling Joists are at the same elevation you will need to use Levels to maintain differences in Joist Heights.
Suppose you have one room that can use 2x6 joists but another room will require 2x8 joists. If both joist sets belong to the same Level and you edited one set to be 2x8 then the other set would change to 2x8 as well.
So the first thing you will have to do before changing the joist set to 2x8 is to assign the set a new Level.
Since Levels are only designated by a number and you can not rename the Level to something informative such as 2x8 @ 9' then you need some other way to keep track of the settings for each Level. Otherwise it is very easy to lose track of Level settings and you can make changes that cause other areas of the plan to change to incorrect sizes or offsets.
What I do is to insert a Table into the Joist Plan and as I define each Level I will fill in the Table with the information about that Level. Then when I am assigning different Levels to different joist sets I can refer to the information in the Table and choose the correct Level.
Bill is the owner and maintainer of SoftPlanTuts.com