I built something similar in shape, but much simpler in design, and it works very well. The plans you posted seem like overkill. I don't know why you would need decking and siding like that. Mine sits next to my garage partly under the overhang of the garage roof. On mine, the logs rest on two upright 2x4's that run the length of the shed and are braced on the ends and in the center. The uprights are 2x4. The roof is a plywood deck on (3) 1x4's attached to 2x4's attached to the uprights and topped with asphalt shingles. I think I used PT lumber for everything except the roof. It's 16' x 6' overall.