I suppose you want something like this:
There is only easy way to do this, and that is to use levels.
Think of levels as you use layers in Photoshop (or Gimp).
I always start my projects with creating three or four levels at the same elevation.
It makes everything easier, believe me.
So here is what you do:
Create three levels at same elevation, and place your walls on level one, your floors on level two
and your furniture on level three.
When your floor plan is ready, create a new level(level four), and set the elevation to match the height of
your walls. Make sure to set the floor thickness to 1.
Then hide level two and three.
Make a copy of level one, and paste it to level four.
Select all on level four and hit shift+cmd+E.
Adjust the height of the walls to 1 cm, and select white texture or colour for both sides.
That's it.
OK?
Cec
