Mái nhà màu trắng.

Yes. Mái nhà means roof or more literally the roof of a house.

• mái = roof
• nhà = house

Together, mái nhà is a very common way to say roof. In many situations, it sounds more natural than using mái by itself.

Vietnamese often leaves out the verb to be when describing something with an adjective or a descriptive phrase.

So:

• Mái nhà màu trắng. = The roof is white.

This is normal Vietnamese. You do not usually add là here.

For example:

• Nhà lớn. = The house is big.
• Trời đẹp. = The weather is nice.

màu literally means color.

So màu trắng literally means white color, but in natural English we usually just translate it as white.

In this sentence, màu helps make it explicit that you are talking about color. It can sound a little more descriptive or emphatic than just trắng alone.

So both of these can work:

• Mái nhà màu trắng.
• Mái nhà trắng.

The first one highlights the color a bit more clearly.

Yes, it is correct.

• Mái nhà trắng = The roof is white / a white roof
• Mái nhà màu trắng = also The roof is white, but with a more explicit color expression

Using màu is not required, but it is very common.

Because Vietnamese usually puts descriptive words after the noun.

In English, you say:

• white roof

In Vietnamese, the usual order is:

• mái nhà trắng
• literally: roof white

In your sentence, màu trắng comes after mái nhà because Vietnamese description normally follows the thing being described.

As written with a period, it is most naturally read as a full sentence:

• Mái nhà màu trắng. = The roof is white.

But depending on context, Vietnamese phrases like this can sometimes also function like a noun phrase, especially in labels, notes, or short descriptions.

So context matters, but with normal punctuation, learners should usually understand it as a complete sentence.

Vietnamese does not have articles that work the same way English a and the do.

So mái nhà can mean:

• a roof
• the roof
• sometimes just roof in a general sense

The exact meaning depends on context.

In a standalone sentence like Mái nhà màu trắng, English will usually translate it as The roof is white if the roof is already understood from context.

A rough guide is:

• mái — somewhat like my, but with a rising tone
• nhà — starts with nh, which sounds like ny in canyon for many learners
• màu — roughly like mow, but shorter and with a falling tone
• trắng — starts with tr, and the vowel is short; it has a rising tone

Tone marks:

• mái = rising tone
• nhà = falling/low tone
• màu = falling/low tone
• trắng = rising tone

The tones are important, because changing them can change the word.

Yes, but it changes the feel a little.

cái is a classifier often used for objects. In many simple descriptive sentences, it is not necessary:

• Mái nhà màu trắng. = natural
• Cái mái nhà màu trắng. = possible, but more marked

You are more likely to use cái when pointing something out, being very specific, or using demonstratives:

• Cái mái nhà này màu trắng. = This roof is white.

So in your original sentence, leaving out cái is completely normal.