Draperies and Top Treatments - Door Panels

I would like to make panels for my french doors. I think I need them to be 30 inches by 68 inches. Do I have to add extra length so that I can gather them in the middle? If so, how much extra do I have to add? I want to order material so I want to be accurate so I don't run short. I have looked on the internet but I can't find any advice for sewing door panels. Any help would be greatly appreciated.

I think you're talking about Hourglass curtains. If you're using a sheer, figure on 3x fullness. As for length, there's two ways to make this. One is making the sides longer and cutting a curve top and bottom, and the other is making a dart in the center, which is the easier method, and you need to add about 18" to the length. There's more involved than just cutting longer and tieing in the center, or you'll have excess fabric hanging. I'd recommend the book "More Creative Window Treatments" by Creative Publishing for the dart method or "Curtains, Draperies and Shades" by Sunset (the older version not the new version) for the curved method.
I'm figuring about 6 yards for each for 54" fabric (or 3yds. if extra wide for sheers) and extra for the tieback. You need to measure and mark the glass on your doors to figure this all out and to know what size tieback you want.