Window Schedule Parameter to show total rough opening area

I'll preface this by saying, I hope this makes sense. I have a client who would like to know the total rough opening that every window creates, and what that total is, because they build tiny homes using SIPS panels. Having said that, is there a parameter I'm missing or one I can create or a way to get my schedule to add up all the window openings in the window schedule? So my RO Width and RO Height would all be added together to create one over all number. The other issue on the schedule is that there are obviously multiple window A's, B's, C's for example. Is this even possible?
Thanks,

(also, how do I delete old attachments? I can't upload new attachments because it says I've exceeded the maximum amount)
Thanks again.

found what I was looking for on youtube. Hopefully this helps someone else.
https://www.youtube.com/watch?v=Gt_khVnmOXs