Create macOS High Sierra 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\ High\ Sierra.app/Contents/Resources/createinstallmedia \
    --volume /Volumes/[volume]
Ready to start.
To continue we need to erase the volume at /Volumes/[volume].
If you wish to continue type (Y) then press return: Y
Erasing Disk: 0%... 10%... 20%... 30%...100%...
Copying installer files to disk...
Copy complete.
Making disk bootable...
Copying boot files...
Copy complete.