What glass to use?

I want to build a replacement "pop-top" for the cabin of a 22 ft. sailboat. My thought is to use the top of the old item as a plug mold for the top of new one; taking the new shell off the mold while as thin as possible and then building the structure up on the inside. I'll use 1/4" balsa for a core and add some sawn plywood ribs, but I'm a bit perplexed by the many weights offered of glass cloth and mat etc. Advice on a lay-up schedule would be much appreciated. I'm thinking of using vinyl ester resin.