what is the limitation of DWG files that can be imported into sketchUp
I don’t think there is a fixed limit per-se, but you could run out of memory on your computer or patience waiting an eternity for the import to complete.
A known limitation is that SketchUp only imports “geometry”, so no text or dimensions. Also, DWG files can contain special objects created by “vertical” applications like AutoCad Architecture (walls, for instance), and SketchUp or any non-Autodesk application cannot import these. SketchUp also seems to sometimes have difficulties with 3D surface or solid geometry that is based on NURBS geometry.