In the northeast we just use plain old red cedar shingles. Lots of guys just put them directly on to the roof, over felt paper and it seems to work fine. I have also seen strapping nailed to the roof, and then the shingles nailed to them to create an air space underneath so they don't curl. Some folks have the whole roof "oiled" so it lasts longer. This should only be done by qualified, experienced roof oilers. You can imagine how dangerous it must be. The old timers all put a large strip of heavy lead flashing over the ridge board b/c the residue that washes off of it tends to keep fungus and/or mildew growth at lesser levels. You notice how much better and cleaner a lot of roofs look directly under a heavily leaded counterflashed chimney. This is b/c of the lead residue. Also, you shouldn't have any overhanging trees so that there is good sun and air circulation. This will help prevent growth and lichens etc. from eating the roof.