It's just house bashin mate but the bloke is so old school that he wants me to do opposites cause he must think u make a better job doing it that way, that's not my opinion but there u go,i do not understand this job.
you can turn an external angle freehand,by rubbing a float in the upright position, repeat the process with a trowel, then pull polythene down the arris, but this would be on a job for someone like english heritage. no on a new build on the rates that you have been quoted.