Hi and welcome to the forum,
TFP will not import a PDF for tracing, only DWG, DXF and JPG. If you save the PDF as a JPG file, either by File/Export in your PDF viewer (if it has that capability) or by zooming the Elevation on screen and the doing a Screen Print (or use the Windows Snipping Tool) and save this as a JPG, then you can import, size and trace that.
However..... I do not see how this is going to help you. The TFP model is 3D and your imported Elevation is only 2D so would be laid flat on the ground, as the Trace option is for tracing the Floor Plan. As you trace, the program itself creates the walls and you add the roof usually with a single click when the outer walls are complete.
Going by the PDF you have attached, the building itself, although not simple, can be done quite easily in TFP and the roof is really quite straight forward, most of it should insert automatically with one click of the mouse, the only modifications needed being to change the automatic Hips it creates, to Gables.
By default the roof will automatically follow the line of the exterior walls so that needs to be done first. I can guide you through the process but you must get the exterior shape right first - the roof will then follow automatically. It will sit at the height nominated as the Wall Height in Settings/Building Locations.
When you are ready to proceed please post an image of your floor plan and a copy of the BLD file (or email it to me if you prefer - alches AT iinet DOT net DOT au).