How To Determine Height and Depth of Foundation Wall?

[geno742]

If you are connecting to an existing monolithic slab, then you must be creating a new slab floor system, yes?
Why not use the slab tool to show it where it goes in plan view. Add the dash line depicting the width of the footing below. You know how deep below grade the thickened edge it must be and make the slab thickness that dimension. It will look correct on the elevations. Use the rectangular polyline box tool to make the section view accurately and you can fill it with the concrete fill pattern. Easy to add the rigid insulation using the box tool again if you need that requirement.

That is how I have been doing it and it looks fine on the construction document page where it counts.