I started by wrapping the shoulder frame in poster board to make a template to transfer to the MDF sheets I am going to use for the "skin". It's an odd shape, so it's much easier to cut poster board to the right shape.
Then I removed the template from the frame and traced the shape onto a sheet of MDF.
Next I attached the new MDF "skin" to the frame with screws in the struts and lots of glue.
I used to same process for the back half. I used a paint brush with a little bit of water to get the MDF to bend into shape easier.