You will need to construct it on a non magnetic frame to prevent magnetic losses. Also select a suitable prime mover to drive the unit. Whether a D.C. motor, Hydro Wheel or windmill. Using this setup means no relative motion between coils and the magnetic field and the disk will accelerate into the permanent magnet poles and slows down on the way out and therefore should result in a steady speed. The voltage is directly related to the change rate of the magnetic field and speed of the rotor.
Amperage is related to how long the pole faces are in position with each other.