Hi user30,
There are two options I can recommend (depending on the desired outcome & PlusSpec version you have), which I’ve outlined below.
Option 1: Currently the size of cornice cannot be adjusted &/or created, so if you want to have different profiles & sizes I could recommend drawing the profile(s) in your model using SketchUp tools & then using the  Custom Estimation Tool to apply an estimating material to each length of cornice.
 Custom Estimation Tool to apply an estimating material to each length of cornice.
This is explained in a little more detail in the post linked below.
Option 2 (PlusDesignBuild Only): You could create a material for each profile that’s named differently so that is appears differently in the takeoff (this is for all version & not just PlusDesignBuild), however, you can also use the override items feature in the takeoff to specify all variations of cornice you want/need. This eliminates the need to create multiple materials (that - in this instance - would just be name changes), so you won’t need to redraw the geometry if a different cornice profile needs to be specified.
Tip: This method can be reused in multiple other areas of the takeoff to save you time.