A Houzz search that might be useful.

http://www.houzz.com/photos/traditional/exterior/query/gray/nqrw

Because there are so many different blacks and grays available, you want to ensure that the grey that you select has an undertone that works well with the under tone of your black shingles. If you have a shingle sample from your roof laying around it might be best to take it along with you to a paint store to look at paint samples. When selecting the paint color, make sure you view it along with your shingle sample outside not in the poor lighting of the paint store.

Hi, I am not a professional but we did just go through choosing exterior paint for our home. You are probably learning there are all kinds of grays with different undertones your lucky that your black roof is IMO pretty neutral! We painted our home SW anonymous gray, which was not my first choice but what my husband and I could agree on, he didn't want gray at all!! Some grays I liked are Chelsea gray, Kendall charcoal, and gray owl Good luck !!

Summit gray or pewter cast from sherwin are pretty nice midtone grays

These are all very nice, just used them on our house...:0)