You can use the free, open-source tool MeshLab to convert OBJ files into a format SketchUp handles more easily, like STL or DAE (Collada).
SimLab OBJ Importer is a plugin developed by SimLab that enables users to import OBJ files into SketchUp. OBJ is a widely used file format for 3D models, and this plugin allows users to bring these models into SketchUp for further editing and design. simlab obj importer for sketchup 2015 crack patched