You want to nail through the peaks of the corrugation when using the panels on a roof. This is because any rain running down will tend to collect in the valleys. Also make sure your fasteners, whether nails or screws, have the sealing washer under the head. Do not overdrive the nails, or you will split the washer and possibly leave a dimple where you can get a leak.
At the crown
There's an under lament that you put (use) in the valleys of the roof. You will nail this no closer then10 to 12 inches from the valley. On the peek of the roof you will cap it .You can either buy the cap or you can make it. To make it you will need a brake(rent one)you cut the size that you need,(no less then25 inches) bend at the center to the pitch of the roof, then nail at the bottom corners so that the nail will be covered with the next piece. There should be directions with the material, if not ask your supplier for them. It sounds hard but it really isn't. Get a few extra pieces just incase of mistakes. Good luck