Just a cpl suggestions to help get you started.........in carpenter lingo,roof pitches are expressed in "rise & run".An example would be.....shingle manuf will only warrent their products down to a 4/12.....this is one reason sheet metal gets the nod on lower pitches.
The 4/12 means that roof is rising 4" for every 12" run,which is simply the horizantal or level,plane.A 12/12 is a 45*,because its goin up 12 for every 12 travel'd on the level.Somewhere around a 9/12....most can't walk on it(steepness).
Next,the nuiance's of roof design can be literally seen from a mile away.Not to mention structural issues.What sounds like a no-biggy shed/shop roof is exactly why so many of them get built by newbs and end up looking.....well.like they were built by a 3rd grader,sorry.I'd say look on the net for info on truss design.Find one thats interactive.....it'll let you play around w/design and dial in the look you're after.BW