We had to do some preparation before putting up the first layer of the roof (OSB.) We had to trim the top of some of the posts because they were sticking up above the angle of the roof. We had to add some blocking in between rafters to give the rafters just a little more strength. We added some metal straps to the ridge beam and rafters for some extra support.
Then it was time to put up a roof! Lifting the OSB that high wasn't as hard as I expected it to be. With one person lifting from the bottom and one person pulling from the top, we would get the OSB onto the second floor. Then two people on the second floor would pass it up through the rafters to someone on the roof (who was, of course, wearing climbing gear and attached to the ridge beam.) Then everyone would put a hand or two on the OSB as the person on the roof put a nail in it to hold it in place. Then, screws and nails were added and we start over again for the next piece.
One side, mostly complete.
We still need to add OSB on the angled edges (but not full sheets) and trim the non-angled edge to 15 feet. (We decided to trim it up in the air so that we could trim the rafters at the same time.) Then, a layer of waterproof tar-paper and then tin. (And, of course, this happens on the other side as well.)