Bennett Feely's Clippy tool is a valuable tool to help make CSS clip-paths.
An excerpt from Bennett Feely's Clippy tool - http://bennettfeely.com/clippy/
The clip-path property allows you to make complex shapes in CSS by clipping an element to a basic shape (circle, ellipse, polygon, or inset), or to an SVG source.
CSS Animations and transitions are possible with two or more clip-path shapes with the same number of points.