In Revit, put the 3d view on a sheet, and export the Revit sheet to .dwg, using "Export views and links as external references". One of the two .dwgs files generated by the Export tool will be the Sheet, and the other dwg file will be the flatten view of the original 3d view.
I have read that there is a "Freeze Drawing" tool that automates this. But I am not familiar with that tool. I think that it needs to be downloaded from the Subscription Center.
