If you mean your own private system and tower sites... you would begin by coming up with the 20-30 million dollars that it would cost (very conservative estimate) to begin acquiring/leasing the land and building the towers sites that would be required to cover 50 Klicks of area. Of course, you could proceed only after filing the approriate site surveys and other applicable county, state and federal licensing applications, building permits, etc. This would just be the bare basics to begin. From start to finish.... you could be up and running in about (5) years or so.
In the alternative; you could just buy some Nextel radios for a couple hundred bucks apiece and subscribe to their Nationwide two-way radio service. Comms between your Nextel radios would be perfectly private, thereby giving you all the functions and performance of your own private trunked radio system: http://www.nextel.com/en/services/walkietalkie/overview.shtml