Modeling recesses is easy, just model a second slab object on the mesh input - standard plan with the reduced thickness, modified elevation and a higher priority where the recess occurs. You can copy and paste if you have a lot of them, or trace a CAD background to make it easy.
The harder part is setting up the design strips and the trimming so that the cross sections that cross the steps are not awkwardly shaped. For more on design strips, see this: Cross Section Trimming