SkUp can export out a DWG - but the model will not be a 'solid' (although it will look like it). Each face of a timber will come in as a 3d surface - OK for presentation - but not useful beyond that. As someone who uses HSB and AutoCad I have not yet found a way to easily convert surfaces to solids.
And - I'm pretty sure you will need the pro version to import / export to DWG.
