How to set nested Associations

I am creating application which requires User management of various
levels for authorization of different level of users.

I want several models:
Admin_user
Project Manager
Company
Clients
Account : have many users of all level.Every user have account.

See below the relations between our models:

1. Admin_user : have many project managers and can give rights to
project manager.It can add and delete Project managers.Admin can
access or manage any level of this application i.e. Its a SUPER USER.

2.Project manager : have many companies.It can create and delete many
companies. Project Manager can also add new project manager if
Admin_user give right to him to create new project manager.its all
depends on Admin_user to give or take rights from PM.

3. Companies : can create and delete many client_users but cannot
create any company in th same level.Company also start or stop rights
of client.

4.Client :can have account login and use services provided by company
nothing more than that.

This is my model Association. But i m confused what can i make first a
Account model or a Admin_user model.

Thanks