Then once you have designed the file in CAD, there are quite a few programs that will allow you to ensure that it is optimized for 3D Printing. Free Slicer programs are out there. But my personal favorite is using 3YOURMIND (http://3yourmind.com) to ensure that the file is prepared for the material I want to print in. I use their integration with Blender (https://www.3yourmind.com/integrations), and with a single click I have the file being verified.

Then I download the file again to create the print. They also connect to 20+ 3d printing service providers so you can also order directly from the site in whatever material you want.