Truss Roof. The only truss roof tool available is the one from vectordepot, but it is not suitable for mono-pitch roofs, you can only use it on roofs that have equal pitches.
Visit vectordepot (http://www.vectordepot.com/older_plug-ins.html) and download the plug-in. Unzip the plug-ins and copy them to your Plug-ins folder. Then you have to add the tools to your workspace.