This is not a custom rom but a mod that would change your phone from its default kitkat rom to Android M. The mod consists of Android M Launcher, bootanimation, Camera, Ringtones, Wallpapers, and more. All these were extracted from Android M Developer preview.
Note: This is meant only for devices running Kitkat and later versions. Your usage of this guide or modification is at your own risk just in case something goes wrong. I will not be held responsible. How to flash/install