Armored duct? I never saw that, but I came up with the same idea. I had a devil of a time working with that thin duct material since I can't bend worth spit. Anyway, here's mine.
It has been completed since then, but that's a 56K safe pic even if it's old. You did a better job of measuring and cutting, I see. Nice edges. I chose to put the edging on the outside to cover up my bad cutting. Hard to get accuracy within 1/16" with a hacksaw for me.