When you need to cut a shape inside a piece of wood, a plunge cut is pretty much your only choice. Typically, you might use a drill with a small bit to bore a hole that you can drop your jigsaw blade ...

I prep each rafter by squaring one end of the board. Rough-sawn and pressure-treated material usually isn't completely square, or it can be rough-cut on the ends. I do this either with a miter saw or ...