Blender is widely considered the best free alternative to SketchUp. It is both free and open-source, offering a comprehensive 3D software suite for modeling, UV unwrapping, texturing, rigging, animating, rendering, compositing, video editing, and Python scripting. It runs on Windows, Mac, Linux, and BSD.
The short answer is to obtain SketchUp Pro 2019 for free, unless you fall into one of the following categories: sketchup pro 2019 classic license free