Roofs have one parameter that offers three options to define a roof edge condition:
- Two Cut - Plumb
- Two Cut - Square
This portion of the Construction Group (groups are the blue "bars, dividing boundaries in the dialog) defines how the roof fascia/edge is adjusted. When you choose either of the Two Cut techniques you need to provide the Fascia Depth value.
Related to this in a way is the setting for Rafter or Truss. This is only available to roofs that have been defined using the Pick Wall technique. Roofs that are not sketched with Pick Wall use the Rafter configuration and do not offer this option in the properties dialog.
I created a short video to show what I'm writing about. As usual I've embedded the video here too so you can listen and watch now.