As for the Purchasing Department, it is also hard to implement the demands of materials needed because they can't always acknowledge these since they also have to see whether these materials are in Bill of Materials and/or if available in the central warehouse. Like what Mr. Remigio have said, buyers should be located at the job site so it can attend the demands of materials and that he/she is always available whenever he/she is needed, hence they will be reporting to the Project Manager.
On the other hand, placing the buyers at the job site would really make a conflict in costs. So in able to avoid this, they will be in charge in communicating to the Purchasing Manager to be informed with the policies and which is which is not included within the scope of materials and funds, before reporting to the job site, so that they will have the knowledge to discuss things to the Project Manager.
In that case, Project Managers have the ability to discuss things to the buyers face to face and buyers have the ability to make amends in contrast with the information and policies given to him/her. After getting the required materials from the Project Manager, they will now head to Purchasing Manager to get the funds for the approved materials.
Project Manager are in charge in managing its subordinate to accomplish the project within the given time and be able to maintain the cost of all materials within the budget. They also review and plan the project span of work and monetary plan and assigns responsibilities to its subordinates.
Administration is in charge with the documents of the site. Which include the...