Thank you for your post.
To create the roof shape you're after I would recommend using the 'Skillion/Shed Roof Tool'
to draw either side of the roof. See image below for more details.
Regarding adding trusses to this roof, I would recommend using the Truss Tool and selection the Skillion Truss option. There's an orange questions mark at the top of the dialog which will take you to a Truss Tool video tutorial playlist. All PlusSpec dialogs have this icon.
Just a heads up that when you're using a tool (SketchUp or PlusSpec), there will be help text that appears a the bottom left of the SketchUp screen. This will show things like shortcut keys and steps outlining how to use with the tool.
Would you be able to please let me know if this fixes the issue your having?