2- Place walls intersection at Internal Origin.
Although you might not care about the coordinate system, you should still place one of the corners of the building at the intersection of the Internal Origin of the project. If you use Revit 2020.2 or later, the internal origin is indicated by the arrows symbol. The internal origin is not to be confused with the Project Base Point and Survey Point, although all these points should be in the same position when you start.
If you export to CAD, this point will be used as the origin. Same thing if you link CAD or another format.
If you are confused about Revit’s coordinate system, make sure to check out our popular guide over here: https://revitpure.com/blog/13-tips-to-understand-revit-base-points-and-coordinate-system
Use shortcut VG to go to the Visibility/Graphics menu. Scroll down to find the site submenu. Check the Internal Origin box. The arrow symbol should appear in your plan view.