The easiest answer is to use an inclined beam with the P steel section or a custom round profile. Beam ends are perpendicular to the ground plane.
For more flexibility also use SEO to create any end shape and subtract. Remember to place the custom profile on a layer you can turn off in order to see the resultant cut away.
Robert,
Add a signature that contains your AC version and OS. You will find the signature in your profile page under Profile Information, make sure to turn on "always attach my signature" in the preferences portion.
Mark