YOU SAID:

they are building a building at the moment.

INTO JAPANESE

彼らは現在建物を建てています。

BACK INTO ENGLISH

They are currently building a building.

INTO JAPANESE

現在は建物を建てている。

BACK INTO ENGLISH

The building is currently under construction.

INTO JAPANESE

そのビルは現在建設中だ。

BACK INTO ENGLISH

The building is under construction.

INTO JAPANESE

そのビルは現在建設中だ。

BACK INTO ENGLISH

The building is under construction.