Post Build Level Loader

Hi,

I am trying to make a game with custom levels. My idea is that after the game has been published, I want to make level files which names will be shown on users installed game version. And if user wants he can download any level to play. Now I have no idea where to start from. My main problem is that the custom levels could contain different assets and also different scripts and I don't know how to put it in a already installed version. It would be like combining several games into one mother application. My target platform is Android. Hope you guys could give me a head start.

Thanks Apratim.