If you're in a hurry, try this trick to elevate the floors of some of the rooms:
- Draw the room with walls all around it
- Give the room a floor
- Give the floor a texture
- Select the floor and at least one piece of furniture that's on the floor
- Use Tools --> Copy as new furniture
- Now use Paste to insert the copy
- Now give the floor an elevation of 50 cms
This is probably the simplest and fastest way to make an elevated floor in your design.
Note 1 - You need to have the plugin CopyAsNewFurniture installed.
Note 2 - It doesn't work if you only use the floor; you need to select at least one piece of furniture in the selection.