There can be many reasons a dog would avoid stairs, including vision or joint issues, tactile sensations, or traction issues. In addition, many dogs lack the back-end awareness that makes stairs and ramps seem passable, especially if the stair depth is shallow or the pitch is steep.
If your dog is generally okay with other stairs, then there may also be other environmental cues (e.g. sounds, smells, or lighting issues) that you are not aware of. Depending on the severity, you may find counter-conditioning helpful.
Stairs in General
Your post doesn't include any concrete information about the stairwell that your dog has problems with. Even if your dog is fine on other stairs, such as those in the park, that doesn't mean that there aren't legitimate problems with the ones in your apartment complex. Especially with German Shepherd Dogs, who are prone to joint problems like hip dysplasia, the depth and pitch of the stairs can matter a great deal.
The surfacing of the stairs (e.g. uncarpeted, metal, wood, or tiled) can also have a big impact. Sometimes it's a traction issue, and sometimes dogs just dislike the feeling of certain materials under their feet. It's up to you to identify what's different about your stairwell that might have an impact.
Improve Back-End Awareness
Of course, once you've ruled out joint and stair-surface issues as causes, the most common reason dogs avoid stairs and inclined surfaces is a lack of back-leg awareness. You may be able to improve your dog's response to stair-climbing by working on exercises that make him more conscious of his back legs.
When going down stairs, the rest of the dog just follows his nose and front feet. Going up a set of stairs, however, often requires a different gait and a lot more confidence and experience with maneuvering the back legs. Teaching your dog to stand on a lower step, or going up one step at a time, could possibly help if this is the issue.
Positive Reinforcement and Counter-Conditioning
So I basically drag him to the stairs (+1 for polished tile hallways) and then he walks down them.
While dragging your dog anywhere might be pragmatic in the short term, it neither builds a bond of trust nor does it reduce the aversiveness of associated experiences and locations. You would be much better served by helping your dog associate positive experiences with the problematic stairs.
A solid foundation with clicker-training would enable you to shape the desired behaviors of approaching, standing on, and eventually climbing the stairs without the need for force. In addition, some basic counter-conditioning such as giving the dog a treat anytime he sees the stairwell might solve the problem on its own, or at least facilitate the use of additional operant conditioning techniques.
As yet another alternative, if your dog is food- or scent-motivated, you might consider leading him up the stairs with a particularly savory something held just out of reach. If the lure is stronger than your dog's aversion to the stairs, then he is likely to follow you at least partway, at which time you can reward him with some of the lure to reinforce the behavior.