Cut steel fascia board cover lengthwise?
I'm not sure what sort of edge treatment you need at the top, but fascia and other light sheet steel can be cut with a sharp utility knife. 

With clamps or a helper, lay a straightedge on the back side of the fascia and score along it with a new knife blade. Knife angle is important and can cause your cut to run astray. Keep things in line. Run the cut twice more, then remove the straightedge and snap the metal along the cut by flexing it. 

If it doesn't fold on the snap right away, and cleanly, score the metal again with the knife. You only need to get maybe halfway through the metal for it to snap. 

If you know someone in the siding or HVAC business with a brake apparatus, cut your metal a bit wide and have them hem it to the final height. A hem provides a safer workpiece and a nicer finish.