Issue Description
Your project features a mezzanine floor with an exposed edge, and you'd like to display this edge with a surface different from the rest of the floor.
Solution
Select the slab and left click on the edge you wish to edit. Open the Custom Edge Settings from the Pet Palette.
From here you can edit the surface color of the selected edges or all the edges at once. You can even edit the angle of the selected edge.
TIP:You can also use the surface painter tool on a 3D View by going to Window > Palettes > Surface Painter.