Are you referring to stern deck solid roof?
When making repairs, modification I have tried to copy duplicate what is there. So If I was going to add on to the roof, I would open up the end of the existing roof with as little damage as possible to be used later for the end of the exstend roof. Also copy the existing roof structure as possible.
I run into Seattle, a coulpe of times each week. Maybe we can hook up and take a look,discuss.