I am going crazy and can't figure this out. 
  
My house has a "barely-attached" garage; it shares a portion of one wall with the house, but all doors are exterior. 
  
The house in on a crawlspace, which is at ground level, so all the rooms in the house are 24" above ground level. 
  
The garage is on a slab at ground level. 
  
The garage walls are 24" taller than the house's walls, so the ceilings are at the same absolute height above ground level. 
  
I've tried creating a foundation of 24" for the house, then making a garage room on a slab, and adding height to the walls.  This doesn't seem to work; I end up with the garage floor being above ground level.  Or the walls are only 24" high and I can't make them higher. 
  
Can someone suggest a specific sequence of steps to make this work? 
  
I want to create a single-story home with a 24" crawlspace and garage on a slab and a deck that is level with the house, but abuts both the house and the garage. 
  
Instructions like this would be enough to get me to understand what I'm doing wrong:   
1. Create a new document 
2. Draw a house in a clockwise direction with exterior walls (ignore the interior) 
3. Draw a garage in a clockwise direction with exterior walls 
4. Set the garage's "room type" to be "garage" 
...etc... 
  
Sorry to be so "needy."  I'm usually a pretty smart person, but this just has me stumped.  I'm very sure of what result I need, but just can't figure out the way to do that with these tools. 
  
Thanks! 
  
Paul