APIs for changing material properties

I am looking to expose the following properties of a material to my users:

  • Opacity
  • Roughness
  • Metallic
  • Bump
  • Double sided

For Opacity, Roughness, Metallic we want them to be able to specify a number.

I am afraid I am not able to figure out the functions to do so. Can anyone please tell me how should I go about this?