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.
I had the same problem with an iMac,
just delete the update program from your mac and re download it from the App Store.
If that won't work you should make a Backup with Timemachine and reset your Mac. Try to update again. if it works, recover your data from the backup.
Check this link if you need help with the reset of your system.
https://support.apple.com/kb/PH25649?locale=de_DE&viewlocale=de_DE
Best Answer
Answering my own question:
From the App Store, grab the High Sierra installer. It will launch "Install macOS High Sierra" after the download completes. Click "Continue", accept the licensing agreement, select the install drive, then the installer will prompt for an admin password. After that, it will begin downloading to "/macOS Install Data" on the local machine.
The main data file is
/macOS Install Data/InstallESDDmg.pkg
When the download is complete, the installer will prompt for a system restart. Before doing that, inspect the download directory:
Then, copy the download directory off to another machine for future use.