This might help. I was looking at doing the same thing, but was having a hard time. I found a lot of information converting google sketch to G-code for cnc. Here is a link to a video about it and the plug-in used.
To be honest, I haven't had time to try it since the computer all the programming was on crashed. I still have to get that fixed before I can try it. I have heard that others have been able to with out a problem. I don't remember what software they used to do the switch though. Sorry I don't have more info on it for you.
I realize this thread is a bit dated but I use Sketchup a lot and there are free Ruby scripts to export your SU design to DXF and other formats. It was built into SU in early versions but Google took it out and now Trimble is further striping capability out of the free versions. I use Google's version 7 as it has the Geo north setting (if you're designing a house not set perfectly N-S) which is now only available on the "Pro" versions.