macOS High Sierra media installer
Massive bump to @IlyaB, I was stumped trying to get the full 5gb Install MacOS High Sierra.app but was stuck with the 19mb stub version.

My Process to get a working app that is currently making my bootable USB for High Sierra

1: Go to Mac App Store and download High Sierra (the 19mb stub)

2: Click Continue in the installer app once it downloads

3: Choose your boot disk (or any disk that has space)

4: Allow the installer to download (this is the contents of the missing "SharedSupport" folder within the installer stub)

5: The installer will prompt you to restart after finishing the 5gb download, at this point quit the installer and do not restart your system!

6: Go to your root (or whichever location you chose in step 3) and find the folder "macOS Install Data"

7: Copy the contents of that folder disregarding .DS_Store  

(9 files, folders, dmgs, pkgs, and plists)

8: Go to your Applications folder where the Mac App Store downloaded the stub version of "Install macOS High Sierra"

9: Right Click on that file and "Show Package Contents"

10: Within the Contents folder, create a new folder called "SharedSupport"

11: Paste the files you copied earlier from the installer download

12: And you're done! You should have a fully functional Installer file for bootable USB drives or just copying to other systems whether they be offline, or you just don't want to download the installer over and over.

I am currently in the lengthy process of creating a bootable USB drive to make a Coffee Lake i7 8700k Hackintosh build. I'm following this guide with the recommended motherboard. I'll try to update here with my success/ failure.