Here's my Foundation Wall Style components from left to right
1,Foundation,1,8",-8",0",Baseline,0",Wall Top
2,Footing,1,1'-4",-1'-0",-10",Baseline,0",Baseline
Now, after you add said wall, it will look like a regular wall. Run the FLOORLINE command, use the OFFSET option with a -10" value. This will show 10" in the negative Z direction, which will allow you to see the footing.
Now, if you make a tool using this wallstyle, simply adjust the properties of the "Floor line offset from baseline" to have a preset value of -10". Now whenever you add that type of wall, if you select it from the tool palette, you won't have to manually do the FLOORLINE command.