I've built the fireplace wall separately for easier application of the brick slips. I had some thick black card which has been perfect to creat a wall and chimney breast. Some of the cornicing has provided a sharp 90 degree angle for the breast. The mantlepiece is 3/16" basswood with strips of cornicing as supports. The whole unit was painted black before the brick slips were applied.
The brickslips are entirely hand made from stipple painting sandpaper with black then red paint (wait for the first colour to dry) and are 3/16" x 3/4".