Roaming je skup.

It breaks down like this:

• roaming = roaming as a noun, usually meaning mobile roaming/the roaming service
• je = is
• skup = expensive

So the structure is:

• subject: roaming
• copula: je
• predicate adjective: skup

In other words, it is a very straightforward Croatian sentence: X is expensive.

Because Croatian does not have articles.

English says the roaming, a service, and so on, but Croatian normally does not use separate words for that. So Roaming je skup can mean something like:

• Roaming is expensive
• The roaming service is expensive

The exact nuance depends on context.

It is a very common loanword from English used in Croatian, especially in telecom and everyday speech.

Croatian speakers often say roaming when talking about mobile phone use abroad. So even though it comes from English, it is normal and widely understood in Croatian.

It is usually treated as a masculine noun in Croatian.

Je is the 3rd person singular present tense of biti, which means to be.

So:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is

In this sentence, roaming is singular, so Croatian uses je.

Because the adjective has to agree in gender and number with the noun.

Here, roaming is treated as a masculine singular noun, so the adjective is also masculine singular:

• masculine: skup
• feminine: skupa
• neuter: skupo

So:

• Roaming je skup.
• Usluga je skupa. = The service is expensive.
• Putovanje je skupo. = The trip is expensive.

This is a very common learner question.

In Croatian, masculine adjectives can appear in a short form and a long form. In predicate position, after je, Croatian normally uses the short form.

So you say:

• Roaming je skup.
• Hotel je skup.
• Telefon je skup.

The form skupi is the long form and is more typical when the adjective comes before a noun in certain uses, for example:

• skupi telefon = the expensive phone / an expensive phone

So:

• Telefon je skup. = The phone is expensive.
• skupi telefon = expensive phone

In this sentence, yes: skup means expensive or costly.

Be aware that Croatian words can have other meanings in other contexts, but here the meaning is clearly expensive.

A useful opposite is:

• jeftin = cheap

So:

• Roaming je skup. = Roaming is expensive.
• Roaming nije jeftin. = Roaming is not cheap.

The most neutral and natural order here is:

• Roaming je skup.

Croatian word order is fairly flexible, so other orders are possible, but they usually add emphasis or sound less neutral. For example:

• Skup je roaming.

This is possible, but it sounds marked and would usually be used only for emphasis or contrast.

For everyday learning, Roaming je skup is the best model.

A simple learner-friendly approximation is:

• roaming: roughly like English roaming
• je: pronounced like ye
• skup: roughly skoop

A few notes:

• Croatian j sounds like English y
• Croatian u sounds like oo in food
• Croatian spelling is generally very phonetic

So a rough pronunciation is:

• RO-ming ye skoop

The exact stress can vary a bit, especially with loanwords, but this approximation is good enough for a learner.

Usually it means roaming is expensive in a general practical sense, often referring to the cost of using your phone abroad.

In real life, speakers may use roaming as a kind of shorthand for:

• roaming service
• roaming usage
• roaming charges

So even if the sentence literally just says Roaming is expensive, the real-world meaning is often closer to Using roaming costs a lot.

Yes, it often can.

Because roaming is usually treated as a masculine noun, Croatian speakers may decline it like other masculine nouns, especially in more careful or formal usage. For example:

• nominative: roaming
• genitive: roaminga
• dative/locative: roamingu

So you may see things like:

• Cijena roaminga je visoka. = The price of roaming is high.
• Pričamo o roamingu. = We are talking about roaming.

In your sentence, though, it is in the nominative because it is the subject: Roaming je skup.

You can add adverbs very easily:

• Roaming je jako skup. = Roaming is very expensive.
• Roaming je prilično skup. = Roaming is quite expensive.
• Roaming je preskup. = Roaming is too expensive.

You can also negate it:

• Roaming nije skup. = Roaming is not expensive.

This sentence pattern is very useful, so once you know it, you can reuse it with many adjectives.