Hi ;
You can cast plaster of paris or spackling compound in a flat tray at a thickness of no more than 1/8" .let it set hard , remove carefully and laying out lines about 1/16' wide take a Fine hack saw blade or Zona saw blade and make horizontal lines across the piece , All exactly parallel .
Then come back in the vertical pattern . If you are at a loss there, go look at a neighbor's brick house for the pattern . Then seal , paint and weather .
The nice part of this is if you think there's too much wall you can always break a piece or two off . Just make sure you paint the exposed edges the right colors . Good Luck . T.B.