1. If your building needs to move in the X, Y, Z coordinate during your documentation process, it is a five update minute job.
2. Due to the limitations of drawing site items in Revit, you can use detail lines and detail components in a site view. This view can then be displayed in whatever views you want in the building file.
Some would say why would you need to have two separate files when you are building on top of an existing building.
Well last week a project architect came to me. He had found an error in the surveyors drawing, where they had given the wrong level for the ground floor slab. So the entire building had been modelled 500mm higher than it actually was. So as it was set up as a building and site file, it literally was a five minute fix.