I am mechanical engineer, and I did a lot of 2D drawings and 3D models in AutoCAD during my professional career.
Most of the time on freelance sites I was drawing house plans in 2D and later I learned to draw 3D renderings of houses and kitchens in Google Sketchup.
I have also deep knowledge in SolidWorks which I used a lot on my previous jobs in several companies where I have drawn conductors, transformers and other equipment in 3D.