Brad28,
Are you speaking about A) cutting away copper (copper voiding) of a ground plane, etc... or are you talking about B) defining a board cutout area that is only for a single fabrication layer (copper/FR4 material)?
If A) There are many ways to void copper from a specific area (defining keepout, using a polygon to define a copper specific area, etc...)
If B) There is no default way, but I suppose you can define one of the mechanical X layers as a custom cutout area and draw the needed cutout shapes on top of the defined board area (and when you export the gerber files, just export the mechanical X layer). You'll likely need to provide special instructions along with the gerber -
Regards,
Pat N
