Download and install Omega 4 theme as you would for any Drupal Theme or use drush cmd in your website folder (Don't install omega tools)
drush dl omega drush en omega
Check to see if you have a version of drush with omega helper commands
drush help --filter=omega
All commands in omega: (omega)
omega-export (oexp) Exports the theme settings of a given theme from the
database to the .info file.
omega-guard (ogrd) Runs guard for the given theme including Compass and
LiveReload by default.
omega-revert (orev) Reverts the theme settings of a given theme by deleting
them from the database.
omega-subtheme Creates a Omega subtheme.
omega-wizard (owiz) Guides you through a wizard for generating a subtheme.
Create a subtheme using drush and follow the prompts
Change directory to your new subtheme and run bundle install to get all gem file dependencies
gem install bundler bundel install
Omega 4x subthemes have a hidden .ruby-version file which bundle install picks up so you will have to edit this file from 1.9.X to the latest version (as of this writing it's 2.3.1). When this is done run
rbenv install –list
This will list all ruby versions install on your machine. rbenv is a ruby version manager if you don't have it on your machine then follow this tutorial on how to install rbenv. If the latest ruby version is listed then proceed below with rbenv install 2.3.1 If the latest version is not listed you will have to do a git pull fron your .rbenv directory in your home folder to get the latest version. Take a look at the install rbenv on ubuntu 14.04 tutorial. All set now we can run
rbenv install 2.3.1
to install ruby 2.3.1 and now you should be able to run bundle commands from your subtheme directory
gem install bundler bundle install
Run drush omega guard to automatically watch your sass folder for changes and apply to css (run from your subtheme directory)