class Company < ActiveRecord::Base
  has_many :projects
  has_many :users

  #used for creation of new companies with related objects
  attr_accessor :new_user
  attr_accessor :new_project
  attr_accessor :new_message

  def initialize(*args)
    super
    self.new_user = self.users.build
    self.new_project = self.projects.build
    self.new_message = self.new_project.messages.build
    self.new_message.user = self.new_user
  end
end

companies_controller.rb

def new
  @company = Company.new
end

in the view, new.html.erb:
you can do whatever you want with them:

<% user = @company.new_user %>
<% project = @company.new_project %>
<% message = @company.new_message %>