Creating a surface coating over part of assembly

Hi.

I'm creating a model of a printed circuit board.  The board consists of the plastic surface with copper tracks and features on top of it (see screenshots).

The grey board is a part, and the copper tracks are made up of different features within a single part in the assembly.

I need to model a coating over the top surface of the board (as I've hand drawn in green on the section view) - so I need to create a surface by offsetting the horizontal surfaces upwards, and offsetting the vertical surfaces outwards and upwards if that makes sense.  I'm presuming the surface coating would be a new part within the assembly.

Does anyone have any idea how I can do this?

Many thanks

Jack

SolidworksParts And Features