Best way to create a pbr Specular/Roughness shader?

Hey guys,

I'm using Substance 3D Painter proffessionally, but a big hurdle for us the that our shading model utilizes a specular colour/roughness workflow. 

Ideally I would like to take the specular/gloss shader and simply replace the glossiness parameter with a roughness one. 

Is this difficult/possible to do? What would be my best course of action seeing as I do not have any glsl experience?