Create macOS Mojave USB Installer

Download the official image from the app store and quit the installer.

Open your terminal and type the following command to create the usb. Use the name of your usb.

$ sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia \
    --volume /Volumes/[volume]
Password:
Ready to start.
To continue we need to erase the volume at /Volumes/Install macOS High Sierra.
If you wish to continue type (Y) then press return: Y
Erasing disk: 0%... 10%... 20%... 30%... 100%
Copying to disk: 0%... 10%... 20%... 30%... 40%... 50%... 60%... 70%... 80%... 90%... 100%
Making disk bootable...
Copying boot files...
Install media now available at "/Volumes/Install macOS Mojave"