A good choice was the use of prefab roof trusses on the 'addition'. I had to get them from a company in Pervis, MS but it was well worth the trip in saving time and money. They each weighed only 90 lbs. So the 2 of us could raise them up in place using methods devised by the Ancient Egyptians. I left the inside open like a 'cathedral ceiling' making it necessary to plan the decking so it looked good. I used T-111, 4 inch separations, 5/8ths thick. A little thicker than necessary but the thinner panels seemed too thin for the adding on of the metal roof. I shopped around and actually saved enough money on the metal roof to pay for the staining and thicker decking. The roof is a light gray metal which actually reflects the colors of the environment, a little green from the trees, a little blue from the sky, and a little red from the sunset. From the ground it is difficult to even see the roof because of the slope it had to be made to, almost flat.
The ceiling is stained a walnut. The first batch was oil stain that made a mess and was hard to clean up. I switched to 'water clean up' stain. More or less a wood preservative with pigment added. It does not penetrate as well as the old fashion oil stain but looks fine when on and cleans up nicely. The problem was color match was off a lot so the wall panels, again T-111, 4 inch pattern but thinner than the roof decking. The color seemed to have a little too much yellow but now I am stuck with it. Inside the pieces match OK as the light is different than outside. The good news is both stains have added properties of UV protection, mold resistance, and water repellent. In case of flood.