Create a subtheme of Omega 4.x in Drupal 7 using drush


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

drush omega-wizard

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)

drush omega-guard