I'm not sure why you feel you must have this done with the slab tool instead of with the beam or wall tool? Complex profiles are perfect for representing pre-cast concrete floor systems.
If modeled with the wall tool, then you just need to make sure that your the layer used for floor slabs has an intersection priority that is different from any of your wall layers.
The only advantage I can think of offhand to slabs is that they permit cover fills...and you can easily cut holes in them with the tool itself for stairs, etc (vs using SEO).
?
Karl