The owner needs to provide the information for the proposed enclosure (mainly material and the possibility). But no matter what, I would make sure the live load is adequate for fully occupied situation with some dynamic effect. Collapse of deck for entertainment setting serving young crowd is not a rare event.
I did one a few years ago and a year later that added a bunch of window-walls. I have not sweat it and eat there pretty often! (The design had a fair amount of reserve strength as it was serviceability controlled) I am surprised the building inspector let them do it.
I've always tended to design as if it is closed in sometime in the future. And that's due to the fact that many times I've seen it get closed in anyway.
It's actually precisely the reason I hate pergolas. People always want them, and then the first time it rains they realize having an open roofed item is not as cool as they thought, so they want to first put a roof on it. Then after the roof is installed they're out there in the spring or fall and realize that it might be nice if they closed it in and could enjoy it as a three season space. Next thing you know, they've converted their pergola into a gazebo. I've honestly seen it more times then I can count.
