Physics swing mass

For my A2 project I need to calculate the GPE of a swing I have made which is just two metal rods swinging back and forth through a thin metal rod with a mass attached to the end. There is also some support on the the top of the swing which adds some mass, but will this affect the GPE? Because although most of the mass is bringing the swing down, there is also the bit of mass on the end which will be counter acting that force. If it will affect it, how do you suggest that I can take the mass to work out the GPE?