Građevinski materijal je skup.

A natural word-for-word breakdown is:

• građevinski = construction / building
• materijal = material
• je = is
• skup = expensive

So the whole sentence means Building material is expensive or Construction material is expensive.

Because građevinski is an adjective describing the noun materijal.

In Croatian, adjectives usually come before the noun, just like in English:

• građevinski materijal = building material
• skupi automobil = an expensive car

So here građevinski materijal is one noun phrase: building material.

It is in the nominative singular.

That is because it is the subject of the sentence:

• Građevinski materijal = the thing being talked about
• je skup = what is being said about it

Both građevinski and materijal are masculine singular nominative here.

Because adjectives in Croatian must agree with the noun they describe in gender, number, and case.

Here:

• materijal is masculine
• singular
• nominative

So the adjective also takes the matching form:

• građevinski materijal

If the noun changed, the adjective would change too.

For example:

• građevinska tvrtka = construction company
• građevinsko zemljište = building land

Je is the 3rd person singular present tense of biti = to be.

So:

• on je = he is
• materijal je = the material is

Croatian normally uses je in this kind of sentence, just like English uses is.

In this sentence, skup is the normal form used after je to mean expensive:

• Materijal je skup. = The material is expensive.

This is a very common pattern in Croatian: after to be, the masculine singular adjective often appears in the form skup.

You should mainly remember:

• materijal je skup = the material is expensive
• materijali su skupi = the materials are expensive

So skup here matches a masculine singular subject in predicate position.

No. Skup can also be a noun meaning gathering, assembly, meeting, depending on context.

But in this sentence it clearly means expensive, because it is being used as an adjective after je:

• Građevinski materijal je skup = Building material is expensive

So this is not talking about a meeting or gathering.

Because Croatian does not have articles like English a / an / the.

So:

• materijal can mean material, a material, or the material
• the exact meaning depends on context

That is completely normal in Croatian.

Yes, materijal is singular.

Here it is being used like a mass noun, similar to English material in a general sense:

• Građevinski materijal je skup. = Building material is expensive.

If you wanted to talk about several materials, you would use the plural:

• Građevinski materijali su skupi. = Building materials are expensive.

Notice how several words change:

• materijal → materijali
• je → su
• skup → skupi

Yes, Croatian word order is more flexible than English word order.

The neutral order is:

• Građevinski materijal je skup.

But you may also hear:

• Skup je građevinski materijal.

That puts more emphasis on skup = expensive.

So the original sentence is the most straightforward, neutral version.

A rough English-friendly approximation is:

GRAH-dyeh-VEEN-skee

A few useful pronunciation points:

• đ is a soft sound somewhat like j or dy
• j is pronounced like English y
• vinski has i pronounced like ee

And skup is pronounced roughly like:

skoop

The adjective skup changes to match the noun.

Examples:

• Cigla je skupa. = The brick is expensive.
• Staklo je skupo. = The glass is expensive.
• Materijali su skupi. = The materials are expensive.

So the pattern is:

• masculine singular: skup
• feminine singular: skupa
• neuter singular: skupo
• plural masculine: skupi

That agreement is a very important part of Croatian grammar.