yeah - I second that. If your sailmaker doesn't have any experience building catamaran sails, I would look elsewhere. Three big names come to mind that would have direct experience building a sail for a Nacra 6.0. This list is not complete but this is where I would start:

Elliot Patterson : makers of most of the factory Performance Cat sails - they do a lot of different multihull stuff and could certainly put together a square head for a 6.0 (they built/designed all the I20 and the older Nacra F18 square head sails).

Calvert Sails : builds a lot of competitive multi-hull (tri) sails and does a good number of beach cat sails...I ordered a Pentex square top main for my ol' 5.2 as well as a new dacron jib from Calvert and was very pleased with both sails.

Smyth : I know he is back making sails but I'm not certain where or what shop he is working out of. Smyth has probably done more beach-cat sail development than any of the other US sailmakers.