gps base and rover

I am looking for a freelancer to help me develop a system that is capable of achieving centimeter accuracy. I have specific requirements in mind, and the system will be used in an urban environment. The ideal freelancer should have extensive knowledge of the latest GPS-based measurement systems and should be able to develop a system that is capable of meeting my accuracy requirement. The ideal freelancer should have knowledge in using the ZED-F9 module manufactured by ublox and knowledge in configuring a base and rover antenna setup.