I have done it many years ago and also internally for floated walls. the thing is when you do it this way everything else around it has to be absolutely spot on otherwise either the render, windows, doors etc etc look like a right bag of sheite. We had it specced on a job in the eighties. did it all Appros 5m high and 20m long in an exsisting building and the clerk of works came in looked a it then got the Architect in and it all got hacked off and done again but, so it was right to the eye and not to a plumb bob. If you have to do it price well for it cos it is time consuming and do it yourself ie do not let a joiner etc you do not know put the grounds in.