Create a triangular profile family using the Profile - Reveal.rfa family template. Create parameters and types for different sizes if you want. Save it with a unique file name. Load it into your project.
Edit the structure of your wall. Turn on the Preview window, and set the preview option to the Section setting. Click on the Reveals button, add a new reveal, set its profile to be the triangular one you created, and set it to be zero distance from the top of the wall.
