There are a lot of roof styles used in buildings today.
Its important when talking to others about your design to use the correct name for a roof style or you will be thinking two different styles.
The first and easiest style is a single Slope or shed roof design. usually associated with more modern designs, but this style is also used on more traditional designs for additions and dormers.
The Gable roof is the most common roof style.
After you know you are talking about this style you need to tell what angle you want the roof to be. Roof angel has been expressed in the number of inches of rise per foot for generations like a 4″ in 12″. What this means is for every 12″ you move horizontally the roof rises 4″ vertically. this was used in the field because every carpenter knew how to use a framing square. the downside is that a 4/12 pitch is 18.43 deg. Now that we use computers and computer added machining I find it easier to round up or down to an even degree. like 20 deg.