While it's not a dedicated program,
why not use http://ncpapaintball.com/field-layouts/
to check out layouts..
You could print just the top down image, and just use that to draw on.
For custom fields, I'm sure you could use a bit of powerpoint ninja skills and make the same thing.
The 'paintball coach' is probably such a small market for developers that I doubt anything is out there, unless someone built one just cause unfortunately