@mblevinsUM3XV though not ideal see the following YouTube work arounds: Thickened Slabs under Walls in Revit 2020
This is very typical detail in a lot of construction project. I'd be lying if I said I was surprised that it isn't in the software already. Is bit frustrating with the lack of actual tools just to produce simple geometrical details and schedules required by arch's, eng's and cad's in a cad software package, and what Autodesk actually gives us every year.
Suppose the simplest and easiest way to do this is to have 2 options available in addition to modifying a slab (current tool which doesn't resolve this requirement) (1) set level/offset above slab and (2) set level/offset below slab using points and lines in a sketch environment. Where you have 2 or more level changes you would select sketch lines/points and set a level on them. The reason for number point 1 is to allow for 2 scenarios.
scenario 1: the slab edge may be raised above the slab top face to a given measurement, thus creating a bit of a wall along the slab edge. The practical real world application this would be perhaps a chemical, petrochemical plant where they are required to contain spillage. In some applications they would cast this raised section at the same time as the sab.
scenario 2: To create a stepped raft foundation as can be seen in typical detail below. The level/offset control would need to allow for negative value i.e. -1234 where a portion may be below the main level of the slab.
This idea would solve quite a number of issues:
1. Beam method level misalignment seen in YT at 2:17
2. Slab edge method on a foundation creates extra work even if profile parametric as seen in YT at 12:02
3. Easily create openings in a slab. Currently slab edges don't allow cutting with an opening as seen in my idea here: Shaft Opening can cut Slab edges
4. More easily schedule data, as current methodologies require multiple schedules creating extra work to derive required data such as total volume.
5. Easier control of visibility graphics eliminating need to create filters ie creating a wall like mentioned above requires a filter to eliminate other wall types out of a view