I would like to get a German Shepherd, but I am out of the house for about 12 hours a day, five days a week. How long can a dog remain in the crate?

In my opinion, this is too long to leave your dog in the crate. If you can put the dog in an outside dog run, then that is OK. But to crate a dog for that long is going to make the dog depressed and/or crazy. In my mind it is inhumane.

You would be better advised to find an adult dog that is 100% house trained. You may have to use the crate for a week or so to get him used to the fact that this is his new home. Then allow him access to only certain rooms and not the entire house.