kositu ha hiroi desu.

It is read:

こしつ は ひろい です。

In rōmaji:

koshitsu wa hiroi desu

A very important point: the particle は is written ha, but when it is used as a topic marker, it is pronounced wa.

Also, in normal Japanese writing, you would usually see it without spaces:

個室は広いです。

は marks the topic of the sentence.

So 個室は means something like:

• as for the private room
• speaking of the private room

Then 広いです says something about that topic.

So the sentence structure is roughly:

• 個室は = as for the private room
• 広いです = is spacious

This is one reason Japanese can feel different from English: the sentence is organized around a topic, not necessarily a grammatical subject in the same way English is.

Because 広い is an i-adjective, and in Japanese, an i-adjective can act as the predicate by itself.

So:

• 広い。 = It is spacious.
• 広いです。 = It is spacious. / It’s spacious. (polite)

English needs is, but Japanese does not need a separate verb here in the same way.

広い is an i-adjective.

That means:

• it ends in い
• it can directly describe a noun:
  • 広い個室 = a spacious private room
• it can also end a sentence:
  • 個室は広い。 = The private room is spacious.

This is different from a na-adjective, which uses な before a noun and behaves differently.

For example:

• 静かな部屋 = a quiet room
• 部屋は静かです = The room is quiet

But with 広い, you do not say 広いな個室.

Because 広い is an i-adjective, and だ is not used after i-adjectives.

Correct:

• 広い。 plain
• 広いです。 polite

Incorrect:

• 広いだ。

A useful rule:

• Nouns / na-adjectives can use だ / です
• i-adjectives use their own form, and です is added only for politeness

So:

• 静かだ / 静かです are fine
• 広いだ is not

Here, です mainly makes the sentence polite.

Compare:

• 個室は広い。 = plain
• 個室は広いです。 = polite

With an i-adjective, です does not change the basic meaning very much. It just makes the sentence more appropriate in normal polite conversation.

So you can think of です here as a politeness marker attached to the statement.

Yes, 個室は広いです。 is grammatical and natural.

It sounds like a simple statement such as:

• in a hotel description
• in a restaurant or internet café context
• in a comparison between room types

That said, without context it can feel a little textbook-like, because real conversation often includes more detail, such as:

• この個室は広いです。 = This private room is spacious.
• 個室のほうが広いです。 = The private room is more spacious.

But the sentence itself is perfectly fine.

The spaces are usually just for learners.

Normal Japanese writing does not usually put spaces between words, so you would normally write:

個室は広いです。

Beginner materials often add spaces to make the structure easier to see.

個室 usually means a private room or individual room.

Depending on context, it could mean:

• a private room in a restaurant
• a private room in a hospital
• a private booth/room in a business or service setting
• a single private room in lodging or housing contexts

So the exact English translation can vary a little by situation, even though the core idea is a room for one person or one group, separated from others.

Sometimes, yes, but the nuance changes.

• 個室は広いです。 = As for the private room, it’s spacious.
• 個室が広いです。 = The private room is the one that is spacious / puts more focus on 個室

Very roughly:

• は = topic / general statement / contrast
• が = focus / identification / new information

In many beginner examples, は is used because it is the most straightforward way to say something about a topic.

Because 広い is an i-adjective, it changes like this:

• 個室は広いです。 = The private room is spacious.
• 個室は広くないです。 = The private room is not spacious.
• 個室は広かったです。 = The private room was spacious.
• 個室は広くなかったです。 = The private room was not spacious.

To make it a question, add か:

• 個室は広いですか。 = Is the private room spacious?

This is a very useful pattern for i-adjectives in general.