I have tried following the Roundearth instructions twice to get CiviCRM up and running on a clean install of Drupal 8, on Ubuntu server 18.0.4. First time through, the installer failed with a permissions error but CiviCRM reported as installed—if there's a way of reverting from this situation, I couldn't figure it out, and I ended up having to start over.
Second time through, it all looked good, but going to any CiviCRM page came up blank. Checking PHP errors, it was maxing out memory. So I increased it to 256, 512, and unlimited—each time, it maxed out on memory (3.2 gigs in the case of unlimited, whereas the server has 4), and I gave up and went home. Only to discover when I got there that the pages now loaded, and continued to load with sane memory restrictions. (???) However, there's no CiviCRM menu (it appears to be there, but empty), and when I go to handpasted admin URLs, things that are supposed to be there according to the docs are blank.
Both of these were with the Roundearth instructions—I found a different set here that I'm trying out, but I don't feel good about it.
I have to deploy a staged site by Friday, and if I can't get CiviCRM to work, I'll plow on without it—but I gather that it really wants to be installed before I start piling on other modules. Any help greatly appreciated.
EDIT: Occurs to me that I have not tried installing Drupal from apt-get (if it's there), because the Roundearth composer script had it included. Could try that next before moving on to the linked instructions. Or not, as apparently it's not in apt.