I second the recommendation for the Vari Kennel. They are pretty tough. They are standard for military dogs. I put a piece of livestock matting cut to fit in the bottom.
Most GSDs will fit fine in the large, but the giant leaves more room to maneuver, especially for a bigger dog.
When a dog saves the life of a man, it becomes clear that partnership knows no bounds.
Fama - T.E.D.D. OEF XI-XII (GSD)
Marshall - T.E.D.D. OEF XII-XIII (Lab)
Lucian - Med Alert (Cane Corso)
Pud - the old man (Pit x Lab)