W ogłoszeniu było napisane, że na poddaszu jest mały pokój do pracy.

Because the preposition w meaning in requires the locative case when it expresses location.

So:

• ogłoszenie = advertisement, announcement
• w ogłoszeniu = in the advertisement

This is why the noun changes form after w.

Ogłoszenie is a neuter noun, and after w in a location meaning, it goes into the locative singular.

So the pattern is:

• nominative: ogłoszenie
• locative: w ogłoszeniu

This kind of change is very common with neuter nouns ending in -enie or -anie, for example:

• mieszkanie → w mieszkaniu
• pytanie → w pytaniu
• ogłoszenie → w ogłoszeniu

Było napisane literally means something like it was written.

This is a very common Polish way to report written information in an impersonal way. There is no specific person mentioned as the writer. Polish uses:

• było = was
• napisane = written

Together, they form an impersonal expression meaning it said / it was written.

A very natural alternative is:

• W ogłoszeniu napisano, że... = In the advertisement, they wrote / it was written that...

Both are correct, but było napisane sounds especially like focusing on the written wording itself.

Because this is an impersonal construction. There is no real subject like he, she, or they, so Polish often uses the neuter singular as a kind of default form.

That is why you get:

• było napisane

not:

• był napisany
• była napisana

Those would require a specific masculine or feminine noun to agree with.

Że means that and introduces a subordinate clause.

So:

• było napisane, że... = it was written that...

It connects the two parts of the sentence:

1. W ogłoszeniu było napisane
2. na poddaszu jest mały pokój do pracy

This is very similar to English that in reported statements.

This is mostly an idiomatic usage of Polish prepositions.

Polish often uses na with certain places, especially ones thought of as areas, levels, or surfaces. Poddasze is one of those places, so Polish normally says:

• na poddaszu = in the attic / in the loft space

Even though English uses in, Polish prefers na here.

Compare some other place expressions where Polish uses na:

• na strychu = in the attic
• na piętrze = on the floor / upstairs
• na uniwersytecie = at university

So this is something you mostly have to learn as a fixed usage.

Again, this is because of the locative case, used after na when talking about location.

So:

• poddasze = attic / loft
• na poddaszu = in the attic / in the loft

The noun changes form because of the preposition.

This is a very common thing that confuses English speakers.

In Polish, after a past reporting verb like było napisane, the next clause does not have to shift into the past the way it often does in English.

So:

• było napisane, że ... jest ... is completely natural

Here, jest presents the content of the advertisement as current or generally valid: the ad says that there is a small room.

If you said:

• było napisane, że ... był ...

that would sound more like the room existed at that past time, but the statement is being treated more historically. In an ad, jest is the normal choice because it describes the property as it is.

Because mały pokój is the subject phrase of the clause and stays in the nominative case.

In:

• na poddaszu jest mały pokój do pracy

the meaning is basically:

• there is a small room for work in the attic

The thing that exists is mały pokój, so it appears in the nominative.

Also, the adjective agrees with the noun:

• pokój is masculine singular
• so the adjective is mały

Because pokój is a masculine noun.

In Polish, adjectives must agree with the noun in gender, number, and case.

So:

• mały pokój = small room
• mała kuchnia = small kitchen
• małe mieszkanie = small apartment

Since pokój is masculine singular nominative, mały must also be masculine singular nominative.

It means a room for work or a room used for working.

The structure noun + do + genitive often expresses purpose or intended use in Polish.

So:

• pokój do pracy = a room for work
• okulary do czytania = glasses for reading
• buty do biegania = running shoes
• maszyna do szycia = sewing machine

It does not mean the room is moving to work. Here do means something more like for.

Because the preposition do requires the genitive case.

So:

• praca = work
• do pracy = for work / to work, depending on context

In this sentence, it expresses purpose:

• pokój do pracy = room for work

Yes, Polish word order is quite flexible.

This sentence could be rearranged in several ways, for example:

• W ogłoszeniu było napisane, że na poddaszu jest mały pokój do pracy.
• Było napisane w ogłoszeniu, że na poddaszu jest mały pokój do pracy.
• Na poddaszu jest mały pokój do pracy, było napisane w ogłoszeniu.

But the original version sounds very natural because it introduces the source first:

• W ogłoszeniu... = In the advertisement...

Then it gives the reported content.

So the original order is a normal, neutral choice.

It is a past passive participle derived from the verb napisać = to write.

In this sentence, it works with było to form the expression:

• było napisane = it was written

So it behaves a bit like an adjective in form, because it can agree in gender and number, but here it is part of a verbal expression.

Yes. Ogłoszenie can mean:

• advertisement
• announcement
• notice

The exact translation depends on context.

For example:

• a property ad = ogłoszenie
• a public notice = ogłoszenie
• an announcement on a board = ogłoszenie

So in this sentence, if the context is housing, advertisement is probably the best translation.