Bei ya chumba ni kubwa.

A word-by-word breakdown is:

• bei = price
• ya = a linker meaning roughly of
• chumba = room
• ni = is
• kubwa = big/large, but here naturally understood as high

So the structure is basically:

price of room is high

Swahili usually expresses of relationships with this pattern:

noun + connective + noun

So:

• bei ya chumba = price of room
• literally, price of the room

This is the normal way to say possession or association in Swahili. English often uses of or apostrophe-s, but Swahili uses this connective structure instead.

Because the connective agrees with the first noun, not the second one.

Here, the first noun is bei.
Bei belongs to a noun class that takes ya in this construction.

So:

• bei ya chumba = the price of the room

Even though chumba is a different noun class, that does not control the form of the connective here. The connective matches bei.

This is a very common point of confusion for English speakers.

Here, ni is the copula, meaning roughly is/are.

It links the subject to the description:

• Bei ya chumba = the price of the room
• ni kubwa = is high / is large

So ni works like is in English.

A useful pattern to remember is:

X ni Y = X is Y

Yes—kubwa basically means big, large, or great.

But languages do not always use exactly the same adjective in the same situations. In Swahili, a price can be described as kubwa, while in natural English we usually say high.

So:

• literal sense: The price is big/large
• natural English: The price is high

This is a normal meaning shift, not a mistake.

Because kubwa describes bei, not chumba.

The sentence is about the price, not about the room being big.

So:

• Bei ya chumba ni kubwa = the price is high
• Chumba ni kikubwa = the room is big

That is an important distinction. The adjective agrees with the noun it describes, and here that noun is bei.

Swahili normally does not use articles like English the and a/an.

So chumba can mean:

• a room
• the room

and the exact meaning depends on context.

The same is true for the whole phrase bei ya chumba. Depending on context, it could be understood as:

• the price of the room
• the price of a room
• room price

In real use, context makes this clear.

Yes. That is another very natural way to express a similar idea.

• Chumba ni ghali = The room is expensive
• Bei ya chumba ni kubwa = The price of the room is high

These are close in meaning, but the focus is slightly different:

• ghali focuses on the thing being expensive
• bei ... kubwa focuses specifically on the price being high

There are two useful possibilities:

• Bei ya vyumba ni kubwa = The price of the rooms is high
• Bei za vyumba ni kubwa = The prices of the rooms are high / Room prices are high

Notice two things:

1. chumba becomes vyumba in the plural.
2. bei often looks the same in singular and plural, so the agreement helps show the difference:
   • ya with singular bei
   • za with plural bei

So the agreement words are very important for understanding number in Swahili.