First, there is no right or wrong model for a PMO. The issue is which PMO type is right for your organization and have you done the proper planning up front before implementing a PMO.
Before you decide on the type of PMO that is right for your company consider the following:
Do you have a Mission Statement for your PMO?
Do you have a Vision Statement (can be covered in the Mission Statement)?
What are the PMO's Principles (what statements will guide how the PMO will achieve its Mission)?
Who are your Customers?
Who are the Stakeholders (those people or groups that will be impacted)?
What are the Goals of the PMO (what does the PMO hope to achieve)?
What are the Objectives of the PMO (must be S.M.A.R.T)?Note: S.M.A.R.T Objectives are (S)pecific, (M)easurable, (A)ttainable, (R)ealistic, (T)imebound
Other things to consider are what Products, Services, Roles and Responsibilities will be offered by the PMO.
Once all of the above items have been finalized you are ready to build a Workplan that outlines the activities to make the PMO a reality.