Here is another example... of a rafter.
Rafters can be tricky in that after drawing them you need to adjust the ends if the pitch changes.

File is here:
www.mikebeganyi.com/webimages/timber/rafter.skp


This is a quick sketch - but I built a rafter that adjusts to pitch and length. I've added guides that you can use to adjust the peak and the foot.

Right click on the rafter and access the dynamic component options. In the box you can change the pitch*, beam height and width, and the rafter run - which is assumed in this case to be the width from the outside face of the plate to the center line of the ridge. The rafter will stretch and the guides will adjust to the pitch.

*Currently pitch needs to be entered in degrees... but I could build in a formula to convert a called pitch (5:12) to degrees.

I've added a variable for the birds mouth - you can tell the rafter how wide the plate is and it will adjust the birds mouth accordingly based on the pitch and the height of the rafter.

After adjusting pitch, length and birds mouth you can edit the component, edit the sub component 'rbeam' to adjust the peak and the foot. (I've given a line on the foot to drag to the interior of the birds mouth, and you can drag the lines around to adjust the peak, etc.)

This is a quick sketch - one could add a variable for stand (if you wanted material above the plate @ the birds mouth), or change the guides to draw a male and female version for a tongue and fork or mortise and tenon joint @ the peak.