Directly from the founder and CEO of Tinkercad is word that they are being bought by Autodesk, and there are “exciting plans for Tinkercad.” The shutdown of Tindercad has been rolled back, people can again sign up for accounts.”
We like TinkerCad because it most of the basic features from SketchUp but has an even lower learning curve and can create “watertight parts” more easily (the parts need to be mathematically solid if they are to be 3D printed).
One can sign up for a free account at http://tinkercad.com/. Best practice is to save your work and export it from any cloud service like Tinkercad soon after completion (just in case the service changes).