I could probably piece one together but I thought I would check on the forum to see if anyone had any suggestions for the easiest way to do so. If you create a triangle shape and extrude it, photoshop doesn't like that. Apparently three sides is too complex a path. If you fiddle with one of the points, curve it just a tad, it will accept it. This creates a triangular tube (I'm sure there's a more accurate name for that). Maybe I could play around with zero depth and punch out the cap.
Work around. My idea worked, but I would like to hear if anyone has a better solution.
(1) Draw your trangle shape.
(2) Convert one of the corners to a smooth corner (just barely). If you doesn't work, bend flex it a little more, and try again.
(3) 3D/New 3D extrusion from selected layer.
(4) Switch camera to top view.
(5) With 3D layer selected, in the coordinates menu of Properties panel, set X angle to 90.
(6) Snap object to ground plane.
(7) Set depth to 0.
(8) In the Cap menu of the Properties panel, adjust cap width to 100%.