Each job is different. How many outlets, switches and other devices are going in the wall. How many wall need boxes in them. if it is only 10 to 15 boxes then I would just pre-assemble the box and length of EMT with a coupling on it. Cut enough stubs for going up the wall with a connector on it. Then just let the mason know where the boxes are going and he may add the stubs in as he goes up with the wall. Labor is maybe 10% more on a small job. On bigger jobs you may have a guy just watching the masons build the walls and need to add the stubs as the wall goes up. This can be time consuming but in the down time the journeyman can be building the boxes and stubs while the walls go up. Another 20% would be a fair assumption for this end.
One thing we do is used colored duct tape on boxes and the stub ups. Brown for lighting, red for fire alarm, orange for e-circuits, blue for data, pink for specialty and good old grey for receptacles. This works out great because its gives you a visual layout of the wall as it goes up and its easy to verify and take the guess work out what is installed.