这句话的主谓宾在那里？

主语The first room I had of my own
系动词 was （这里确切来说不能称为谓语）
表语a small one

I had of my own 是定语修饰room
only 5 by 4 meters square 是对屋子小的补充说明

是 I had of my own 修饰room,
因为主语是The first room,谓语是was，宾语是a small one.

主语是room,是定语从句.
the first room that I had , that 可以不用.

I had of my own 修饰room，Room是主语，was是谓语