The rental office I'm in is on the first floor of a rental apartment building.
The office I rent is located on the first floor of an apartment building with rental units.
この場合、次のような言い方ができますよ。
ーThe rental office I'm in is on the first floor of a rental apartment building.
「私のいるレンタルオフィスは賃貸マンションの１階にあります」
on the first floor of a rental apartment building で「賃貸マンションの１階」と言えます。
ーThe office I rent is located on the first floor of an apartment building with rental units.
「私が借りているオフィスは賃貸マンションの１階に位置します」
the office I rent「私が借りているオフィス」
ご参考まで！
カナダ 
