I end up having to hide the slabs and draw them correctly using the line tools. Not only is this a waste of time but it also means that I have to use non 3D elements which don't update as you work in with model. Thus, I must remember to change the lines when I modify the slab and I can't use the story setting to make them display on other floors.
There's the rub.
The implementation could be very simple. When you click on a segment of a slab with the slab tool active the pet pallet pops up and one of the icons could represent hide line segment. When selected it would hide the selected segment by changing its pen to white, dotted, or 91 in plan (so it can be seen of editing) and hide it altogether in the 3D Window and when printing.
Hiding a line is a very reasonable wish, as it is the way most 2D and 3D polygons work in GDL as it is. The pen and linetype idea is more futuristic. I personally could live w/o it if I could hide lines.
Another possible implementation could be for segments to auto hide when two slabs share a segment line and the slabs are the same thickness, height, and have same floor and ceiling materials.
It is a long-standing wish and, I presume, GS's goal, to have all contiguous, same-material polygons clean up in 3D. In plan, I'm skeptical. If these are slabs which represent plan-visible stuff (floor finishes?), shouldn't you have a line where there's a change? And to show the material pattern you still need fills. (Fills-on-slabs-etc. may be the oldest wish there is.) If they are 'structural' slabs, their visibility should be handled with layers.
Also why not let us apply different materials to vertical edges of slabs individually?
I wished for this for years. It became less urgent when solid element ops came about. If you subtract from an element using 'Inherit attributes of operator', you can individually control the material of edges and holes.
Good, thorough wishing.