The Steam Controller has been released, and it sold out in just a few minutes, so now people are waiting for a restock. According to Engadget, Valve has now released the CAD files for the gamepad's shell, and it's free to download under a Creative Commons license. This means that people can now design and construct their own accessories for the Steam Controller.
But there is a small catch. The files are only for the device's exterior, so you won't be able to 3D print yourself the innards to build your entire controller from scratch. We just have to be patient while waiting for a restock for the Steam Controller.
Valve hasn't given a release window yet for the Steam Machine and Steam Frame VR headset, which means that the Steam Controller might not be an essential purchase right now.