kono tatemono ha rippa desu.

この means this, but it must be followed by a noun. So:

• この建物 = this building

You cannot use この by itself. If you want to say this alone, you would use これ instead.

• これは立派です。 = This is splendid/impressive.

は marks the topic of the sentence. In この建物は立派です, the topic is この建物.

So the sentence is structured like:

• As for this building, it is impressive.

This is a very common Japanese pattern:

• A は B です = As for A, it is B

Both は and が can mark something important in a sentence, but they do different jobs.

• は introduces the topic
• が often marks the subject more directly or adds emphasis/new information

With この建物は立派です, the speaker is talking about this building as the topic and then describing it.

If you said この建物が立派です, it would sound more like:

• This building is the impressive one
• or it may emphasize this building in contrast with others

So は is the more neutral, standard choice here.

立派 is a な-adjective.

In Japanese, な-adjectives can be used in two main ways:

1. Before a noun

   • 立派な建物 = an impressive building

2. At the end of a sentence

   • 建物は立派です = The building is impressive

That is why there is no な in your sentence. The な only appears when the adjective directly modifies a noun.

Because 立派 is not directly modifying a noun here. It is being used as the predicate of the sentence.

Compare:

• 立派な建物 = an impressive building

  • here 立派 modifies 建物, so it needs な

• この建物は立派です = This building is impressive

  • here 立派 comes before です and finishes the description, so there is no な

です makes the sentence polite.

So:

• この建物は立派です。 = polite
• この建物は立派だ。 = plain / less polite

In this sentence, です does not add tense by itself beyond the present/future-style copula use; it mainly gives a polite tone.

The plain form is:

• この建物は立派だ。

In casual speech, people may also simply say:

• この建物は立派。

That sounds conversational and informal.

建物 is read たてもの.

It means building. Literally, the kanji are related to:

• 建 = build
• 物 = thing

So it is basically a built thing, which is why it means building.

立派 is read りっぱ.

It can mean things like:

• splendid
• fine
• excellent
• impressive
• grand

For a building, 立派 often suggests that it looks impressive, grand, or dignified, not just pretty.

So this word has a stronger nuance than something like simply saying it is nice.

Yes, it is completely natural.

It sounds like a straightforward, polite description of a building. For example, someone might say it when seeing a large temple, government building, school, or impressive house.

It has a slightly formal or respectful feel because 立派 is a fairly strong, positive word.

The spaces are usually just for learners.

Normal Japanese writing would be:

• この建物は立派です。

Japanese normally does not use spaces between words the way English does. Textbooks and beginner materials often add spaces to make the sentence easier to read.

Then you would say:

• この立派な建物

That means:

• this impressive building

Notice the difference:

• この建物は立派です。 = This building is impressive.
• この立派な建物 = this impressive building

So when 立派 comes before the noun, it needs な.

Yes.

These are all part of the same demonstrative pattern:

• この = this ... near the speaker
• その = that ... near the listener / already mentioned
• あの = that ... over there, away from both

So you could say:

• その建物は立派です。 = That building is impressive.
• あの建物は立派です。 = That building over there is impressive.

The grammar stays the same; only the location/relationship changes.