I was talking with a Revit user the other day that was having trouble placing a Truss object in their Revit Structure. After they placed the truss, it would disappear even though all visibility settings for the view were correct in allowing it to display. Needless to say, the user was frustrated. The problem was that there were no members defined for the truss, so only the truss’s reference lines were visible when the truss was highlighted.
A truss is a special type of family which requires information to be input within the project before the truss can actually be seen. The following illustration shows the appearance of a highlighted truss that does not have any Structural Framing members assigned to it:
Structural Framing families must be loaded into the project file for trusses to have members assigned to the truss. (Any Structural Member families in the project may be assigned to the truss.) If no Structural Framing families exist in the project file, use the Load Family function (from the Insert menu) and select the Structural Framing families that are desired for the chords and webs of the truss.
After Structural Framing members are loaded in the project, highlight the truss and select the Edit Types button in the Properties palette. By default, the “Structural Framing Type” parameter will be set to “Set Framing Type“. (If no Structural Framing families exist in the project, then the “Set Framing Type” value will be the only option available.) Specify the desired structural framing family for each chord and the webs.
The following illustration shows the appearance of the Type Properties for a truss with no Structural Framing members assigned and the locations where the user must define the members:
The following illustration shows the values available for the Structural Framing Type parameter with two different Structural Framing families loaded:
The following illustration shows the appearance of a truss after having Structural Framing members assigned to it:
Note: If the truss still does not display, delete the truss and place it again after Structural Framing members have been assigned to the truss.
Applying Technology to Architecture 
Any thoughts on how to make a truss where each diagonal can be a different size? I’m having to mimic an existing design for an addition to an industrial plant. The new trusses will be the same as the existing ones. My first pass through, I just modeled them as beams and columns for the diagonals. Columns were required for the verticals. I made it a model group and then copied away. The connectivity is causing fits. Now, the roof elevation needs to change and all the trusses basically implode. This has me trying to go back and look at the truss feature again, but it’s just very hard to work with.