After the walls have all been assembled the roofing edge boards go up next. They just need to be alligned with the edge of the wall that its going on and then nailed. The picture below shows how its placed.
The boards that go on top need to be placed on to the pieces that are on it now, depending on the shed you have the pieces that go on it varie. But they basically just need to get nailed on for shingles to go over.