|I'm quite happy with how this roof came out|
So I decided to experiment. I lightly sprayed the roof paper on the back (non-lined) side with gray primer from a spray can. After drying I had a uniform gray roofing material. Too uniform though. So next I took flat black spray in a can and misted that over the gray. Just far enough to not fully coat it. A few larger drops of black appeared here and there, so I misted more gray over the black to blend it together. The results were just what I wanted. A black roof that has been subject to a quite bit of sun which caused fading. I did not even need to do any additional weathering with chalks or paint.
I cut the sheet on the scribed lines (now on the unpainted side) and used transfer tape to apply to the roof. Any bad areas that had a paint drop that did not look good I worked around. Plenty of material to discard sections. I really think the look is good, better than most of the roofs I have done. I do like a few of the dark and light spots that appear that look like stains. The effect is real nice in person.
I'm glad I was able to turn a pretty mundane material into a nice looking roof for this building. A few more details and this one will be done.