You can always use the auto roof feature if you want.
Otherwise I would suggest using the hipped roof. Just put the arrow at one end of the roof and drag it across to the opposite corner. If you don't like it you can always undo.
Roofing is one of the harder skills, and the roof tool is not very flexible. You probably have to try several different things before you find something you think is good.
Don't forget that you can stack roofs on top of each other, as well as, adjust the hight of either one, or different roof sections.