Truss layouts transform to fit the full span of the truss, creating framing elements that correspond to the lines in the transformed truss layout.
Open a view of the building level where you want to add the truss.
Click Structure tabStructure panel (Truss).
On the Properties palette, from the Type Selector drop-down, select the truss type.
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.