I would like to build a faux stone cover for two utility boxes (phone box
and cable box) in my front yard. I saw they sell these online - but they are
very expensive and not the ideal sizes I need.

I thought about building a wire frame and covering it with some kind of
plastic resin material, then spraying it with stone speckle paint - but
specific directions or recommendations would be very appreciated.

I'll most likely plant small bushes around it when complete.