Here's an interesting modelling challenge set by Nilanjana of the London Office. She wanted to quickly produce a balcony, based on the sketch below, for a large high rise residential scheme.
You will see from the diagram above that the majority of the balcony is 450mm deep and is flat as indicated by the blue area. The balcony then falls away on three edges to only 150mm thick. You will also notice the balcony is not rectilinear as indicated, with three sides at different angles.There are a number of different ways to tackle this.... create a family, an in-place family? All have their merits, but at the concept stage of a project you don't always have time to produce what in essence is actually a rather complex family to create. So the easiest way to create the balcony is in four separate elements.
So start by sketching out a few reference planes to define the extent and shape of the balcony.
Next create a new floor slab type which is 450mm thick. Edit the type properties of the construction of the floor slab and set the structure "variable" radio button is ticked. This will ensure that that slab is flush on the underside after you have edited the slab.
Next model four separate slabs based on the reference plane sketches.
You can then slab edit the edges of the three slabs which need to slope away using the sub-element edit tools. Select one of the floor slabs you created and the sub-element edit tools will appear in the options bar.
Next select the edit points/edges tools, then select the outer edge of the slab you want to edit and alter the elevation from 0mm to -300mm; this will drop the whole edge of the slab and it will slope as required.
Now do this for all the other edges which need to fall away.
For extra finesse, use the join geometry to clean up all the floor slabs.
One could argue that this is not a purist approach to the BIM problem because you end up with four slabs rather than one, but at that concept stage where you want to convey an idea, this approach is ideal.