Over the weekend I gave some thought to my design constraints/goals for a 12 ft top beam. Due to space it has to be pushed up against a wall in my Garage. Also, I prefer that the wall not be weight bearing and I have be able to level it on a uneven floor with almost a 2 degree slope.
I came up with the idea of building a rafter rotated 90 degrees so the ridge line is on the floor. With speed square in hand, I penciled in 15 degree plumb lines and birds mouth cut. I confess I had to consult the little blue book and watch a youtube video to jog my memeory. 
I will support it on the wall with two ledger boards that are attached to the studs, and will level it with some 2x or plywood feet (not shown).
On the bottom stringer board, I will drill out 1 inch holes for dowel rods that can slide forward and back to support the sheet material that is being cut, and on the top of the 4x8 have holes for dogs or clamps.
The top beam will be super strut that can be adjusted to the proper chain angle.
Comments, suggestions always welcome.
Thank you