In the RW, the bulk of labor for large scale construction projects consists of migrant and transient workers. The number of workers at any given time will vary - often quite drastically based on scope and current stages of constructions...
The original question doesn't have a single valid answer - especially with TL and government types considered.
However, the size of the shipyard could determine the size of permanent workforce - the management and skilled labor requisite for undertaking the scale of shipbuilding a shipyard is capable of producing. Dave's approach should suffice for the technical side of things... with the larger bulk of the direct and indirect labor labor force determined by other factors. (How many to build a section of hull is dependent on method of obtaining resources - asteroid vs strip mining - working the resources - smelting/casting/welding - and local work regulation and organizations such as unions, government work programs, migrant policies, etc.)
The construction capacity of a shipyard may be dependent on the size of the local and temporarily available (in-system or interstellar) workforce. The capability of a shipyard (ala drive TL manufacturing) would affect the requisite size of the shipyard.