My favorite workflow for importing cad files is as follows.
I export from cad in controlled chunks. Meaning I export the topo first, then the sitework like sidewalks, parking lots, etc. I import those separate portions into SketchUp and deal with them one by one.
I first run Todd Burch's "Make Faces". This goes through and makes faces of all the linework that it can find. It often leaves lots of faces unclosed, typically because the linework does not import from cad cleanly enough.
So, to clean up the linework, I like to use "Stray Lines". It might be a little tedious, but once you get the hang of it, it goes by quickly. This script label every line the does not connect to another line. Typically those are lines that connect in autocad, but lose their connection in SketchUp. It is then a matter of going around and either connecting each line that is labeled, or deleting the tiny line segment if it slightly longer than needed.
Then I rerun makefaces. And then anything that still won't turn into a face, I being troubleshooting by drawing lines across the surface where the face should be. Eventually it will start closing in some places, some places will not close. Keep doing that until you can find exactly where the troubled line is that is keeping the face from closing. Then fix it.
And then once I get that done, I begin to import the next portion of my cad work.
Smustard does have some great tools that speed up that process. One is close opens, the other is delete short lines. Both of those can be very useful for automating the process I go through in the step where I label all stray lines. Those two scripts will delete all tiny edges that typically are not needed, or will auto-extend a line if it is a short distance from another edge and appears like it should just be a closed line.
Anyhow, good luck!
Chris
