I had some trouble finding a method on the interwebs that made sense to me for this project, so I thought I would put this out there in an effort to help others that are looking for options.  We didn't want holes in the ceiling of our container, and we wanted a robust attachment to build from to withstand high winds and heavy ice build-up that can occur in the Ozarks.  We ended up deciding on 10' wide x 36' long x 8.5' - 9.75' tall for plenty of storage/parking and quadruple the rain water collection than our existing set-up.  Setting the header 3.5" above the roof line leaves a nice attachment surface for a future roof deck.

More videos to follow as we make progress on the build.  Hope it helps.

God bless.