I'm not sure of what you mean by invert? You want the shape to be a hole? If that's that, you only have to create a solid (being your composition size), place it under your shape and use the track matte menu of your solid, with alpha.
Julien is right if you do it with a solid layer under the shape layer. You can also do it all in the shape layer by essentially doing the same thing except instead of making a solid layer, you make another shape path and use the merge paths with the mode set to subtract.