Bill,
I have tried it both ways and definetly would sugggest you glass your deck first before building your cockpit recess and combing.

You can do it either way, and both will work, but one is easier. One you get your combing up I suggest you consider glassing it too before you sand it back and apply your combing lip. ( I recommend a Japanese rasp for this) I have just posted below a response to Pete Rudies Sharing of a materieals strength graph. In it is a suggested schedule for glassing combings. orienting your weaves for more strength.

Use thicked epoxy to lay up your lip. It better then glue I think. Then after you have laid up your lip put the third layer of weave in a third orientation between your combing wall and lip. This schedule gives you a lot of strength around the most delicate part of your boat. The part that operationally sees the most point torque and the part that has the most material transitions. Its a good part of the project to give a little extra strength too across a broader set of vectors.

Enjoy the process

!RUSS