I came across an article from Steve Stafford’s blog about Revit likes to alter the nearly horizontal/vertical line in your imported CAD file; for example, a line drawn at 89.57 degree in AutoCAD is altered to 90 degree in Revit without any warning. So be very careful the next time you decided to trace your dwg file to start your model.
Here is the link to the article:
Dwg Import – Lines Nearly Vertical/Horizontal are Changed, from Steve Stafford’s blog
The translated version to Persian here: http://irancad.com/newsdetail-386-fa.html