Float a floor inside a garage with varying stem wall heights..Is it possible?

[zowie123]

Hi all,
Converting a garage that's 12" below main level.  Stem walls vary around garage. 

Tried creating a stair landing, but can't draw the closet walls on a stair landing.  

 

So then created a slab--can draw walls on that, but doors bounce around because they don't have a solid reference point and of course the slab won't frame like a floor which means time wasted later. 

 

The floor structure tool in combination with balloon framing tool when hanging the floor above and below stem walls of differing heights is death by way too many clicks.

 

Anyone have a simple way to do this?  

 

It seems if we were allowed to build walls on stair landings it would be a major evolution. 

 

Thank you,

Barry