YOU SAID:
He is building a boat himself
INTO JAPANESE
彼は彼自身ボートの建物は
BACK INTO ENGLISH
He has his own boat building
INTO JAPANESE
彼は彼自身のボートの建物
BACK INTO ENGLISH
He is building his own boat.
INTO JAPANESE
彼は彼自身のボートの建物です。
BACK INTO ENGLISH
He is building his own boat.
Come on, you can do better than that.