It is a 2D CAD application for drafting and detailing. We've designed it to be a really good companion application for SketchUp (and for AutoCAD). The UI is very similar to AutoCAD so that it should be easy to learn if you know AutoCAD's classic interface. It's not an AutoCAD LT clone, but is a "work-alike" with some differences in the feature set.

DoubleCAD XT is a full featured CAD application without limitations -- and it's free. Use it for unlimited commercial or personal purposes.

It has very good .dwg filters, but also reads .skp really well. Your .skp comes in with all layers and proper visibility; it automatically creates a paper space from each scene in SketchUp; all SketchUp components are automatically converted to DoubleCAD blocks. DoubleCAD includes an ADT-compatible wall tool, and all those DoubleCAD blocks (read .skp components like Anderson Windows, etc) can be dropped into the self-healing walls, and they automatically self-align.

If you save the file as a .dwg and bring it into AutoCAD or AutoCAD LT, the walls, and all the blocks you brought in from our application, retain their self-healing abilities in AutoCAD too! So you might just want to use DoubleCAD to kick-off projects you draft more fully in AutoCAD. You could also use the wall tool to kick-start your SU projects. Draw out the walls, then explode them, save them as a .dwg, and import that into SU -- it's a pretty quick workflow.