It goes on from there.....the homes will (supposed to)follow city and state codes for construction.
These codes can vary in dif. geographical locations (Oregon- California) have dif. codes........in addition to this they change all the time; some builders will overbuild to a higher spec (Cal. spec on an Oregon home).
The way pluming is run throughout, dif. construction materials used can change(copper, iron, P.V.C. braided hose).
Consider that the builders don't always use the same routing methods or measurements!
Your guys should keep in mind that at times they will find an interior wall that will be filled to the gills with scrap SHEETROCK that they must figure out how to overcome.