This is the 8274th most frequent Japanese word.
建
"建" means "build" or "construct."
The word '建てた' here is the past tense of the verb '建てる', meaning 'to build', denoting the completed action of constructing the school.
この学校は建てたばかりです。
This school has just been built.
The word '建物' is a noun incorporating '建', referring to 'building', here used to ask about its structure.
建物の構造は何ですか？
What is the structure of the building?
The word '建てた' is used metaphorically here to mean 'establish', showing that the concept of building can extend to abstract constructs like theories.