So I found this video this morning via Luke Johnson on twitter who runs whatrevitwants blog. This is a YouTube video describing the project coordinate system in Revit. There are a lot of potential problems to run into when dealing with the coordinate system. This video gives a good overall and detailed explanation of how to set up the system in your Revit project. The authour of the video cwm9 on YouTube also discusses: Project and survey points, coordinates, clipped and unclipped modes and finally true north settings in Revit.