It depends on a lot of factors. First, what kind of fans are you planning to use with it? You'll need to consider the fin spacing (lower fpi for less airflow), core depth (thinner for less airflow), height and width (does it need to fit inside the case or an external radiator box? Larger for lower airflow), and spacing between tubes, to name a few things. I'm assuming you're trying to make a tube and fin radiator, though I don't know how you would manage that easily.
This thread should be fairly helpful if you're looking for a low-noise design.
Since you're designing this for a very specific use, and probably not for mass production, you should strongly consider finding fans that exactly meet your requirements, then build the radiator to best match those fans.