The building is tall. The shop isn't. It's just as tall as any other office sitting on the first floor.
It does sound weird in Hungarian, too. But you never know... Grammatically it is good.
Maybe they are selling huge chandeliers, or cranes.
What if there is a 3-floor building, and the store occupies all the floors.
Because the üzletek are described as being magasak and not nagyok.
A nagy épület could be big without being tall (for example, by being very wide instead).
Could it mean "high", for example shops that are in the top of a tall building or on a mountain?
No. The structure of the sentence (missing "vannak" and the adjective in plural) clearly shows, that the "magasak" is an attribute of the "üzletek". What are they? They are some tall buildings.
The question was not whether magasak is an attribute of the üzletek but whether magasak in this sentence could refer to something that is located at a high altitude, rather than merely something that extends to a high altitude.
Yes. What I wanted to know is whether this adjective always means great in vertical extent or also great in vertical distance. "High" means both. "Tall" only means the former. I guess I got my answer.