"Nem, ez nem magas ház."

Translation: No, this is not a tall house.

[IvanEb]

Can this not be "No, this house is not tall." ?

[vvsey]

No. Just like in English, that is a different sentence in Hungarian:

"Nem, ez a ház nem magas."

In one sentence, "magas" ("tall") is just an adjective, in the other it is part of the predicate.