Sorry to hear about your carport problem. Sounds pretty complicated if the shed is already in place. If you were doing that from scratch and need another couple feet of height, I would say mono slab or small continuous footing and three courses of 8"block. Run the top course as a lintel block. Make sure you have some rebar doweled into the slab or footing and then pour the walls solid striking the top smooth. The rail of the shed can be attached to the top of the 2' tall wall. If your shed is already in place, I would pick up one side carefully and build the wall under it. Set down one side on the top of the wall and pick up the other side and build the wall. This should take 90 block per side or 180 block total plus a total of 5 CY Concrete for the Footings and 1 1/2 CY for the wall. Lot of money for 2 feet.
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