Hello Nathan,
Park-domain options are available in cPanel as well as in WHM, through which you can park a domain to a particular account.
If you want to make your own park domain scripts ( function ) and want to integrate it with cPanel then you have to use some cpanel function.
It is it a bit complicated, because cPanel updates daily which will result into breaking of your customized scripts.
Hence, I'd recommend you to use the inbuilt scripts provided for free by cPanel/WHM.
