I suggest that you look at some material on the proper way to do it. Most of the roll roofing I have seen on barns and other roofs that are not flat does not have asphalt on the nail lines.
Look especially at the last Atlasroofing link above.
Roll roofing will last a long time if properly applied but it looks terrible if you make a mistake. Shingles are a lot more forgiving from an appearance point of view.
Applying heavy roll roofing is not a one-man job. It is very difficult to get it properly aligned and nailed without bumps and humps.