Thanks for the reply. Yes, the area on the left of the shaded area is currently garage and I will be framing a floor over the slab. The existing roof structure will remain. The current garage slab is -14". The new front garage will also be at -14" relative to top of subfloor. The walls in red are existing in the basement. I am not planning on changing the slab or foundation of the existing garage. I want to draw the garage foundation with the slab 4" below the top of stem wall. This is where I'm really having trouble. I know I could re-build the foundation and add the interior walls again. In this case that wouldn't be too time consuming but I am trying to learn if I can create the proper garage foundation without rebuilding.