Using rooms in the past has sometimes been a real pain. Especially on large complex projects with multiple split levels. I've spent hours trying to get them to display properly. Much of it was not really understanding how rooms work. The use of badly positioned room separation lines did not help. Errors in rooms seem to fill the error warning screen. These can eat up memory and I've seen a project where rooms and room separation lines were removed and the file size fell by 30 to 25 MBs.
Thankfully there has been some changes in Revit 2009 which should help. The settings dialogue box has even changed names: What was a "Room and Area Settings"
is now "Area and Volume Computations"
Notice how the "At specified height" has been removed in the new settings. It now just defaults to 1200mm height. You have no choice. Take a section through a room and select it, and you will see the 1200 line.
So the Room area is calculated at 1200mm off the level it is hosted to.
One of the new settings that helps you define a room is it gives you the following error if the base of the room is above the 1200 level. This should help users to not make errors when positioning rooms in split level buildings (always make a level for each split level and put the room on that level).
In addition to this, now when you select an element in Revit that is causing an error, a warning icon comes up in the option bar which will assist in solving issues.
You will also notice that you can now do color schemes in section views and rooms can fit the room shape, if the volume setting is turned on, in the "Area and Volume Computations" settings.
Be warned on this however, turning on the volume setting will cause a lot of number crunching within the model. Not advisable for large models.
Despite all this, I've still had some rooms not behaving correctly.