kono tatemono wa katsute koukou datta.

topic particle

Breakdown of kono tatemono wa katsute koukou datta.

• この: this
• だ: to be
• 建物たてもの: building

Questions & Answers about kono tatemono wa katsute koukou datta.

How is this sentence read aloud?

It is read:

この たてもの は かつて こうこう だった。

Word readings:

• 建物 = たてもの
• 高校 = こうこう
• だった = plain past form of だ

What does この mean here, and why not これ?

この means this and must be followed by a noun, so この建物 means this building.

By contrast:

• これ = this one / this thing
• この建物 = this building

So you cannot say これ建物.

Why is は used after 建物?

は marks the topic of the sentence. The topic is この建物 — as for this building.

So the structure is roughly:

• この建物は = as for this building
• かつて高校だった = it was once a high school

This does not always translate naturally word-for-word into English, but that is the basic grammar.