It's not an easy issue. I bought double doors made of wood (oak) with a lot of glass. They cost $5500 five years ago. I face south, but there is a roof over them so they get no rain or exposed sun. There is a slight bit of warpage. I wish the movable door (both move, but there are top and bottom bolts on one) were secured top and bottom instead of just the middle like our French doors by Andersen. They would close tighter. I might be able to fix that with different hardware, but the Baldwin mortised hardware that they used cost a bloody fortune as it is.
I originally asked about fiberglass doors. As it turns out, they are easier to finish, but they contain wood and therefore are NOT warranted against warpage. Same was true of the so-called "metal" doors. Really nice wood doors are upwards of $25,000. You can build a small house for the cost of some of them.
Let us know what you find.