I have a dog, I love dogs of all shapes and sizes.
I am not sure why you chose a German Shepherd to keep in an apartment, there are so many dog breeds to choose from, and to be honest German Shepherds would be way down the list of suitable dogs for apartment living. Greyhounds are great, as they sleep for about 22 hours a day.
There are some suggestions here that you claim the dog is an assistance animal – the thing is, some people are scared of dogs, and you need to bear in mind there may be residents who find the presence of a German Shepherd upsetting. It works both ways.
You say that you had the permission of the agent and the landlord to keep a dog, and a verbal assurance from the building manager. The landlord should have sought permission from the owners corporation for you to keep the dog. Have they done that?