Here's a cross section drawing of my final design. It's cantilevered from the sloped ceiling of my attic/bedroom. The green 2x4 block lays flat against the ceiling and is the point of attachment. Attached to the 2x4 is a long 1x2 1/4" and short vertical 1x2 that ties them together. An L girder of 1x2s runs lengthwise across the front. Decked with 1/2" plywood, everything is glued and screwed. I'm building in sections so if I ever get a better location the benchwork can be removed and the mounting brackets sawed off. It's a pretty narrow shelf (12")but narrow benchwork is far better than no benchwork at all. Any thoughts are welcome.