TrussMaker

TrussMaker is a built-in tool in ArchiCAD which allows you to create truss objects
With line tool draw the frame and if you use different pen colours this will help you to define different cross-sections later in trusmakker settings dialogue box.

Select all the lines making up the truss and and go to Design > Design Extras > TrussMaker

After customizing the truss hit OK and than save.

This will be saved as a new truss object inside your Embedded library.