Some time ago, I helped out on a project that had a lot of slab depressions that seemed to keep on changing all the time. The problem was in their setup; the sketch of the main slab had to be edited to create a void, after which a new slab with a negative offset was modeled inside that void. Lastly, a slab edge had to be added matching the depth of the slab depression, after which all elements had to be joined so the section would read cleanly. Certainly a few steps too many, and that's when I get unhappy.
It didn't take long to create a rectangular and an L-shaped stretchable generic model that creates a slab depression and performs all the above mentioned steps at once.
The geometry was based on this structural detail, and adapts to the thickness of the host slab.
For starters, I created types for 1”, 2”, 3” and 4”.
If a section is cut through them, joining the slab and the depression family will clean up the linework.
The files can be downloaded here (2013).