I want to customize existing odoo erp module

General information for the business: project management
Kind of development: Customization of existing program
Num. of modules: 4
Description of every module: 1. Project Module: create a sub projects with unique id from a parent project. This project is linked to Budget Module
User-right defined for 3 different roles
2. Create a Budget Module linked to account and project to track payment for all suppliers
3. Customize Sales Module to be linked to Project and Purchase Module
4. Create Purchase Module to be linked to Project, Budget, Budget, Sales, Purchase, and Account module using new custom fields PO number and Site ID on all these modules
Description of requirements/functionality: For every project or Sub Project created there exists PO number and Site Id which is the linking parameter to the Purchaser order(Puchase ),Sales order(Sales Module), Invoice(Account) and Budget Module
CMS and Admin requirements: create roles for Validator, Approver in Purchase Module, Sales Module, Budget Module and Invoice Module
Specific technologies required: Python,Odoo 8/Open erp Frame work
Extra notes: additional may be added as required