Morphed objects?

Hi everyone, I’m new to SketchUp and started to use it for 3D printing. I’m sure this has been asked before but I’m trying to figure out or find a tutorial on how to make a 3d object for example that is hollow with 2mm walls and is a circle at one and changes smoothly to a square at the other end. Any ideas?

Thanks alot!

This sort of question comes up often. A search will turn up a number of threads. Start with these: