You have the option to change the geometry of slabs with vertex points.

Vertex points

For you that are unsure what, vertex point is, they are the blue marks around the geometry of the objects, there is a difference between a breakpoint  and an middle point .

For a breakpoint, you have the following options:

For middel points, you have the following options:

When you want to add vertex points you have to be aware of where the vertex points are added from the point that you selected.

When selecting a breakpoint to add a vertex, the new vertex point will be placed on the line right side of the breakpoint.

When adding a vertex point by using a middle point you break that line.

Model space

Based on the information above, changing the shape is quite straight forward.

Slab definition

You also have the option to add vertex points under the endcap tab along with assigning endcaps to the sides in the edit slab pop up window. But when you have added the vertex you have to move the points to where they belong.

First of all, we need to understand how the selection works in the endcap tab when adding vertex points.

The selected line is the one that is going to be added vertex point.

When the vertex point is added press enter and you will get back to the endcap tab where you can select the next line that needs adding vertex point