Shingles and rolled shingle material are suitable for roofs here in New England that have enough pitch to allow gravity to drain the water down and away from the material. I have run across several Dormers, porches, add/ons, that were constructed with roofs that have 3 in 12 pitch or less , and yet they are covered with shingles or the rolled material of the same construction. The results are always the same, leaks, stains, mold. The area is usually not accessible from the ground with field glasses, as it is a second floor, and the pitch is almost flat. The rolled material also has a much shorter life than regular shingles, tending to crack and leak.
As an owner, one should get several estimates from reputable roofers on price, as well as the type of roofing that is required for the pitch of the roof. If all 3 are saying that you should use a rolled rubber roof, then that is the proper roof for the pitch! Getting a permit from the Town and advice from the building inspector wouldn't hurt either.
As an inspector, one must make every effort to see what's up there, if accessible. If not you must be clear to the client what portion of the roof has not been seen, and hence is at risk. Asking for receipts, etc, is a good way to scope out what has been done, and who did it!
Not all roofs have the right pitch for the geographic area, i.e., snow and ice accumulations, so do your homework before you get ripped off, especially on flat or near to flat roofs.
