there are several approaches to the extent that you do not want to use a seperate glass tape on the outside and use the deck glassing to also overlap/join to the hull. but the two basic varieties are:

1) to the extent that the coaming is recessed and sitting on its own plane, you would just glass that plane and build out your coaming or at least the risers and glassing the risers. this way when you do glass the deck, you have a clean crease to mate up to. in this technique, as you glass the deck, you would cut a hole in the cloth for the coaming so everything would sit right as you are wetting out.

2) build out the coaming (risers and coaming) after you have glassed the deck onto the hull.

in either case...its important to think through all the steps ahead to be comfortable that your sequencing will not create any extraordinary difficulties and to do as much inside work as reasonably possible while halves are still apart and easy to access the inside. that said, my preference would probably be number 2. i don't feel that there was a lot happening under the deck when i did the coaming that made that overly difficult.