Why aren’t you working with a design professional on this? Terrible idea. Worse than owning a black car in Miami. The added heat gain, oil canning, and almost immediate fading from UV, ought to have you wondering why your builder didn’t immediately tell you no. Other than green is the only color he cares about and would agree to put in a purple roof if you paid the green.

Find an architect to design the house that a builder builds. And don’t let builders have design input unless it’s about cost consequences.

Most metal roof manufacturers sell a black color of their roofing.

They're of a particular color and finish that increases its reflectivity while still being black, but without getting over heated.

Weather and dirt will appear on any metal roof. I have essentially permanent pine needles on my (black) metal roof, and it's not a problem to me. It's just a part of having a metal roof.

Rain washes the dirt and leaves away. Wind blows more on.

What climate do you live in? As Live_Wire_Oak mentioned, your heat gain from a black roof will be significant. Even in a cold climate (like I live in) this will be an ongoing challenge for your HVAC and comfort. It’s a myth that black is better for melting snow on your roof. The white snow actually reflects away much of the sunlight, so the dark roof underneath doesn’t get the chance to melt the snow in a significantly faster speed than if the roof were not black. The trend is toward lighter colored roof shingles to avoid heat gain demands on your HVAC, and the extra insulation your attic will need as a consequence.

I would go with that dark slate color instead of straight up black. Although I recall people's houses having black shingles when I was a kid.

Hard pass on a black metal roof. Or large expanses of black exterior anything for that matter, depending on where in the world you're at.