I believe he is also going to put a back piece in and that would give an enclosed box with 2 adjacent sides being open. The top cornet would not have any support under it from just the wood. You would need to either put something under that (like a metal frame - that extends across the entire unit) or support it from above (say with a cable). The problem with the first is that cables stretch and the cable itself would be unsightly. Therefore the only other option you really have is support from underneath.

Ram, feel free to call me and I can discuss this with you further in detail. Your employer has my cell phone number. It is listed under Rimrock Reef.