I need to make a rafter for a storage shed that is 10 feet acrossed and I need about 4 inches hanging over each side. The roof pitch needs to be 6/12. I really don't understand what that means. Does that mean 6 feet high to a 12 foot length? Anyway I need a roof pitch of 6/12 and it has to be 10' 8" across. What and how do I start? Thank you.