I have a metal / tin roof. I think it works great. Some people think it is to noisy when it rains. I've had no problems with my birds, at all. I had a very good breeding season, and the noise from the metal roof doesn't seem to bother the birds at all. I had gotten some breeding stock from a guy. The birds where a couple of years old , and they settled quite well, going down on eggs with in several weeks.
As for painting the roof black.... I would not. My metal roof is a light tan and during the day, it gets warm even hot. I have a tin roof on my Chukar pen, it is gray in color and it gets very hot. In my opinion, if you were to paint your roof black, you would get your loft way way
to hot. I have my roof screwed right into the trusses.
As for the hard sheet insulation. I live in Pa, it get pretty cold here. I didn't use any insulation in my roof or my loft. The biggest thing you need is ventilation in your loft, but keep drafts down as much as possible. The cold drafts will get your birds in trouble/sick. This is only my opinion again. Maybe we will here some other opinions on this topic.....
And another thing about a metal roof, i like is, the ability to use the clear plastic panels as a sky light.
Here are some pic's of my new breeder loft. In the first pic you can see the plastic panels / sky lights. The second pic is the start of the breeder boxes half done. You can see all the light that comes in with the skylights. The pictures were taken in Feb.
I hope i helped a little.