Just reading through the Attic Truss information it may not be possible to do automatically. However that does not mean it can't be done.  Chief can define the envelope but you may need to do the webbing pattern. If you open the Truss Detail and unlock the Framing, Roof Trusses layer you can work on the webbing manually.  You will need to use existing members and edit and rearrange them or copy within the same detail. Angles can be mitered using a general framing member and the Trim and Extend t