Pond design should be based on lay of the land. Step one, ask the NRCS to come out and survey your elevations. They can provide topographical maps and aerial photos, also. Finding the best area to build a dam may be different that building it where you want it. After the best site is picked, have the dam site staked out, using wooden surveyor stakes. Then, using surveyor's flags, outline the proposed water line. See how large your pond will be. Then, it's time to start talking to earthmovers.
One of my favorite phrases comes into play, here. "Remember, you will build a dam, but you will also create a lake." Those are two different subjects. The dam is a water management tool, a lake is a habitat.

Teach a man to grow fish...
He can teach to catch fish...