The airlines insist on the plastic crates which I think are more like the natural den a dog would choose. They also want the the dog to be able to stand fully erect in it, maybe even a Shepherd's ears. You might check the websites of airlines you are likely to use. The description of a crate should include if it is airline approved.
If your Shepherd is average or large, you may need a huge one. Check some different brands.
How old is your Shepherd? If not over a year, check the ends of the leg bones. If they are still much knobbier than an adult's, the growth plates are still open and it is still growing. If not, do not expect much more growth.
You may find this link interesting,
http://jn.nutrition.org/cgi/content/full/134/8/2027S
