قاعة العرض كبيرة.

In Arabic, the present tense of to be is usually not stated.

So:

قاعة العرض كبيرة
literally works like: The exhibition hall big

but it means:

The exhibition hall is big

This is called a nominal sentence in Arabic.
If you wanted past or future, Arabic would use a verb:

• كانت قاعة العرض كبيرة = The exhibition hall was big
• ستكون قاعة العرض كبيرة = The exhibition hall will be big

The sentence breaks down like this:

• قاعة = hall / room
• العرض = the display / the exhibition / the presentation
• كبيرة = big

Together:

• قاعة العرض = the exhibition hall / the showroom
• كبيرة = is big

So the structure is:

• قاعة العرض = the subject
• كبيرة = the predicate describing it

Yes. It is an iḍāfa construction, often called a genitive construct or noun-noun possessive structure.

Literally, it is:

• قاعة = hall
• العرض = the display/exhibition

So:

قاعة العرض = hall of the exhibition/display

In natural English, that becomes:

• the exhibition hall
• the showroom
• sometimes the display hall, depending on context

In an iḍāfa:

1. the first noun comes first
2. the second noun specifies it
3. the first noun does not usually take ال
4. the whole phrase can still be definite

Because in an iḍāfa, the first noun normally does not take ال.

So Arabic says:

• قاعة العرض

not:

• القاعة العرض ❌

Even without ال on قاعة, the whole phrase becomes definite because the second noun is definite:

• العرض = the exhibition/display

That makes قاعة العرض mean the exhibition hall.

Because it means the display/exhibition here, and in this iḍāfa it helps make the whole phrase definite.

Compare:

• قاعة عرض = an exhibition hall / a display hall
• قاعة العرض = the exhibition hall / the showroom

So the ال on العرض matters.

Because قاعة is a feminine singular noun, and the predicate adjective agrees with it in gender and number.

• قاعة is feminine
• so the adjective must also be feminine singular
• therefore: كبيرة and not كبير

Compare:

• المعرض كبير = The exhibition is big
• القاعة كبيرة = The hall is big

Even though العرض is masculine, the word being described here is قاعة, not العرض.

Because here كبيرة is not an adjective inside the noun phrase. It is the predicate of the sentence.

So:

• قاعة العرض كبيرة = The exhibition hall is big

But if you say:

• قاعة العرض الكبيرة

that means:

• the big exhibition hall

That is just a noun phrase, not a complete sentence.

So the difference is important:

• قاعة العرض كبيرة = complete sentence
• قاعة العرض الكبيرة = noun phrase only

In fully vowelled formal Arabic, it would be:

قاعةُ العرضِ كبيرةٌ

Here is why:

• قاعةُ = nominative, because it is the subject of the nominal sentence
• العرضِ = genitive, because it is the second part of the iḍāfa
• كبيرةٌ = nominative, because it is the predicate

In normal everyday writing, these endings are usually omitted:

قاعة العرض كبيرة

A careful formal pronunciation with case endings is approximately:

qāʿatu l-ʿarḍi kabīratun

In normal pause-style pronunciation, you will often hear something closer to:

qāʿat al-ʿarḍ kabīra

A couple of useful pronunciation notes:

• ق is a deep q sound, not an English k
• ع is a throat sound that English does not have
• the ة in قاعة is heard as t in the iḍāfa: qāʿat al-...
• the ة in كبيرة at the end is usually pronounced as -a in pause: kabīra

Because both words end in ة (tāʾ marbūṭa), but they are in different situations.

• In قاعة العرض, the word is connected to another word in an iḍāfa, so the ة is pronounced as t
• In كبيرة, the word comes at the end of the sentence, so in pause it is usually pronounced as -a, not -t

So you often hear:

• qāʿat al-ʿarḍ
• kabīra

This is very common in Arabic pronunciation.

The normal, straightforward order is:

قاعة العرض كبيرة

This starts with the subject, then gives information about it.

Arabic can sometimes change word order for style or emphasis, but for a learner, this is the standard pattern to use:

• subject + predicate

So this sentence is a very good model for simple descriptions such as:

• البيت كبير = The house is big
• السيارة جديدة = The car is new
• قاعة العرض كبيرة = The exhibition hall is big

You would say:

قاعة العرض الكبيرة

Here الكبيرة is a true adjective modifying قاعة العرض, so it becomes definite.

Compare carefully:

• قاعة العرض كبيرة = The exhibition hall is big
• قاعة العرض الكبيرة = The big exhibition hall

This is one of the most important distinctions in Arabic sentence building.