I decided to live in the same building from the end of June.
"6月末から同じマンションに住む事を決めました"
- I decided to live in the same building from the end of June.
- I have decided to live in the same building as you guys from the end of June.
- Starting from the end of June, I will be living in the same apartment building.
I'm going to be living in the same apartment building as you from the end of June.
You and I will be living in the same condo starting the end of June.
この場合、次のような言い方をすると自然な感じで良いですよ。
ーI'm going to be living in the same apartment building as you from the end of June.
「6月末からあなたと同じマンションに住みます」
ーYou and I will be living in the same condo starting the end of June.
「6月末からあなたと私は同じマンションに住みます」
ご参考まで！
アメリカ合衆国 
カナダ 
