I have a line of covered runs 14' deep by the length of my chciken building, but no pics at the moment, I will see if I can get some. It is just built shed-style, self-supporting and not actually attached to the main building.
(I did not build this, it was preexisting, and I really would advise AGAINST the structurally-separate design unless you feel cornered into it by building permit regulations, because what happens to ours is that it moves a little with frostheave and opens up a gap between the two that has been a chronic major leak into the runs for YEARS, although I believe I've finally got it more or less licked. If you DO do a structurally-separate thing for your run roof, at least have LARGE roof overhang from the upper roof to give you more margin for error!)
As far as engineering, basically you are building a shed. Engineer it as such, then put wire instead of siding on the walls and add extra diagonal bracing to restore the stability lost in the lack of rigid sheathing. Wall-less shed, roofed run, same thing
BTW I highly recommend it (large roofed run) in SO many ways, you won't regret it!
Good luck, have fun,
Pat