Όταν η συγκάτοικός μου γυρίζει αργά, δεν κάνω θόρυβο στην κουζίνα.

It means when, but in this sentence it has a habitual sense, so in natural English it can feel like whenever.

Because the verb is in the present tense, Όταν η συγκάτοικός μου γυρίζει αργά means something like:

• When / Whenever my roommate comes back late...

So this is not about one single event only; it describes a repeated situation.

γυρίζει is the present tense, 3rd person singular, of γυρίζω.

Greek uses the present tense very often for:

• habitual actions
• repeated situations
• general truths

So η συγκάτοικός μου γυρίζει αργά means my roommate comes back late as a usual or recurring thing, not necessarily she is coming back late right now.

For a one-time future event, Greek normally uses a different verb form after όταν:

• Όταν η συγκάτοικός μου γυρίσει αργά, δεν θα κάνω θόρυβο στην κουζίνα.

So the contrast is:

• γυρίζει = she comes back late / whenever she comes back late
• γυρίσει = when she comes back late on a specific future occasion

That is a very important pattern in Greek.

συγκάτοικος means roommate or flatmate.

It can refer to either a man or a woman. The article shows the gender:

• ο συγκάτοικος = male roommate
• η συγκάτοικος = female roommate

In your sentence, η tells you the roommate is female.

Greek normally keeps the definite article with this kind of possessive expression.

So:

• η συγκάτοικός μου = my roommate
• το βιβλίο μου = my book
• η αδελφή μου = my sister

This is one of the big differences from English. In Greek, my is often expressed as:

article + noun + weak possessive pronoun

So the article is completely normal here.

Because μου here is a weak possessive pronoun, and these usually come after the noun in Greek.

So Greek says:

• η συγκάτοικός μου = my roommate
• το σπίτι μου = my house

Not normally:

• μου η συγκάτοικος

For an English speaker, this may feel reversed, but it is the standard Greek pattern.

The basic word is συγκάτοικος.

When a word stressed on the antepenultimate syllable is followed by an enclitic word like μου, Greek often adds an extra written accent:

• η συγκάτοικος
• η συγκάτοικός μου

This is just an accentuation rule. It does not change the meaning, case, or gender.

Yes, γυρίζω can literally mean turn, but in everyday Greek it also very commonly means:

• come back
• return
• go back

So in this sentence, γυρίζει αργά means comes back late.

A more formal or more neutral verb would be επιστρέφει, but γυρίζει is very common in normal speech.

αργά is an adverb here, meaning late.

It describes how / when she comes back, so it modifies the verb γυρίζει.

Compare:

• αργός / αργή / αργό = slow, late as adjectives
• αργά = slowly / late as an adverb

In this sentence, with γυρίζει, the meaning is clearly late.

Because κάνω is an indicative verb form, and Greek uses δεν to negate indicative statements.

So:

• κάνω = I do
• δεν κάνω = I do not / I don't do

Greek uses μη(ν) mainly with:

• imperatives
• subjunctive forms
• certain non-indicative structures

So in this sentence, δεν κάνω is exactly what you want.

Yes, absolutely. κάνω θόρυβο is a very natural Greek expression.

It breaks down as:

• κάνω = I make / do
• θόρυβο = noise

The dictionary form of the noun is ο θόρυβος, but here it appears as θόρυβο because it is the direct object of κάνω.

So:

• κάνω θόρυβο = I make noise
• δεν κάνω θόρυβο = I don't make noise

στην is the contracted form of:

• σε + την

So:

• στην κουζίνα = in the kitchen / to the kitchen

Here the meaning is clearly in the kitchen.

A few useful points:

• σε is a very common preposition that can mean in, at, to, depending on context
• Greek normally uses the accusative after σε
• κουζίνα is therefore in the accusative form here: την κουζίνα

Also, Greek usually includes the article in expressions like this, so στην κουζίνα is more natural than just σε κουζίνα.

Greek word order is fairly flexible.

The sentence as given is very natural:

• Όταν η συγκάτοικός μου γυρίζει αργά, δεν κάνω θόρυβο στην κουζίνα.

But you could also say:

• Δεν κάνω θόρυβο στην κουζίνα όταν η συγκάτοικός μου γυρίζει αργά.

The core meaning stays the same. What changes slightly is the emphasis or flow.

When the όταν clause comes first, Greek normally separates it with a comma, as in your sentence.