How do I add a custom script to ubiquity source code that will create a few new folders on desktop when the installer finishes?

Question

edit: I need to do this manually by tampering with the ubiquity source code, not with the help of some tool like Ubuntu builder

I need to have a few new folders and files be automatically created once ubiquity installation is complete.

Where do I add a custom script that can do this in the ubiquity source code?

Any sort of help will be much appreciated. Thanks.