Are there any existing PSD or Sketch (preferred option) files for Material-UI components available?
I can use Sketch build in Material Design Template v2 for mockups but I am not sure if that is an accurate representation of the components for prod design. And that is something that can cause issues later on.
http://www.sketchappsources.com/free-source/1601-material-design-sketch-template-v2.html
Material-UI has an official version for Sketch, they are an accurate representation of production and kept in sync with the React components.
Alternatively,
Sketch has a few symbols for Material Design but they cover very few of the components and an outdated version of the specification.
Material Design has a Sketch plugin but it supports fewer components than Material-UI and doesn't use the same wording/structure as Material-UI that makes it harder to move from design to implementation.