It's called a shed style roof. Want it not to leak, have enough slope so reguler shingles will work, have the birds mouths cut right the first time and have the angled cuts fit flush, not have it sag.
Then hire someone to frame it in for you.
It sounds like a simple job but I've yet to see a first time DIY build one right.
Not trying to give you a hard time.
Google "shed style roof" most of the web sites will say the same thing.