What choices do you have?
I would stay away from red as I think it would be TOO much red with the brick. Green? Too much like Christmas probably. But in some Googling, I found several suggestions that a very dark green would look good with red brick.
Here is a site that lets you try colors on a brick house, though their brick is more worn (less red) looking:
Metal Roof Color Visualizer | Best Buy Metals
There are applications on the Web that allow you to upload a photo of your house and experiment with different paint colors -- Sherwin Williams is an example. It might be worth Googling to see if there are applications for roof colors.
Steve
dark green would look good. are there houses around you like yours with metal roofs that you could look at?
google images for brick house with metal roof.
Id go Dark Brown, Different enough from the Brick to contrast, yet complimentary to the overall colour.