If you're sold on going with a black steel roof, you might want to look into the Kynar (sp??) that is available.  Guaranteed to not fade for (I think) 40 years.  Neighbor put a generic black steel roof on his garage about 20 yrs ago and it is now kind of a gray-green color.

I agree that a black steel roof could be real hard on the attic and could even make it harder to keep the rest of the house cool in summer.