Revit transforms the truss layout to fit the span of the truss and creates framing elements that correspond to lines in the transformed truss layout. For more information, see Creating a Truss Family.
To add a truss
Open a view of the building level where you want to add the truss.
Click Modify | Place Truss tabDraw panel (Line) to specify the start point and endpoint for the truss, or click (Pick Lines), and then select an edge or line to which you want to constrain the truss model.