Ο υπεύθυνος ορόφου εκκενώνει τον όροφο.

Because ορόφου is in the genitive case. In this sentence, υπεύθυνος ορόφου means the person responsible for the floor or the floor supervisor/warden.

Greek often uses the genitive where English uses of:

• ο υπεύθυνος ορόφου = the person in charge of the floor
• literally: the responsible one of the floor

So όροφος is the basic dictionary form, but after υπεύθυνος you need the genitive: ορόφου.

Greek does not always repeat the article in expressions like this.
Here, ορόφου functions closely with υπεύθυνος to make a title-like phrase:

• ο υπεύθυνος ορόφου

This is very natural in Greek. It works a bit like:

• director of sales
• head of department
• floor manager

You could think of it as a compact job-title structure. The article appears before the main noun υπεύθυνος, not necessarily before the genitive noun that follows.

They are different cases of the same noun όροφος:

• ορόφου = genitive singular
• όροφο = accusative singular

They have different jobs in the sentence:

• ο υπεύθυνος ορόφου = the supervisor of the floor
  Here ορόφου depends on υπεύθυνος.
• τον όροφο = the floor
  Here όροφο is the direct object of the verb εκκενώνει.

So the sentence uses the same noun twice, but in two different grammatical roles.

Here is the breakdown:

• Ο — masculine singular nominative article
• υπεύθυνος — masculine singular nominative noun/adjective used as a noun
• ορόφου — masculine singular genitive
• εκκενώνει — verb, 3rd person singular
• τον — masculine singular accusative article
• όροφο — masculine singular accusative

So:

• Ο υπεύθυνος ορόφου = the subject
• τον όροφο = the object

It is originally an adjective, meaning something like responsible. But in modern Greek it is also very commonly used as a noun, meaning:

• person in charge
• manager
• supervisor
• responsible person

So in this sentence, ο υπεύθυνος is functioning as a noun: the person in charge.

This kind of adjective-to-noun usage is very common in Greek.

εκκενώνει is the verb form meaning he/she/it evacuates or is evacuating, depending on context.

Grammatically it is:

• present tense
• active voice
• 3rd person singular

The base verb is εκκενώνω = to evacuate / to empty out

So:

• εκκενώνω = I evacuate
• εκκενώνεις = you evacuate
• εκκενώνει = he/she/it evacuates

Greek present tense can describe:

• a present action
• a habitual action
• sometimes a more general statement

Because the subject is singular:

• Ο υπεύθυνος ορόφου = the floor supervisor / the person in charge of the floor

That is one person, so the verb must also be singular:

• εκκενώνει = he/she evacuates

If the subject were plural, the verb would be plural too.

Yes, Greek word order is more flexible than English because the case endings show each word’s role.

The neutral order here is:

• Ο υπεύθυνος ορόφου εκκενώνει τον όροφο.

But Greek could also move things around for emphasis, for example:

• Τον όροφο εκκενώνει ο υπεύθυνος ορόφου.

This might sound more like:

• It is the floor that the floor supervisor is evacuating or simply put focus on τον όροφο.

Even when the order changes, the articles and case endings help you understand who is doing what.

The dictionary form of a masculine noun is usually the nominative singular:

• ο όροφος

But when that noun becomes a direct object, Greek usually puts it in the accusative:

• τον όροφο

So:

• ο όροφος = the floor (subject form)
• τον όροφο = the floor (object form)

This is one of the most important things for English speakers to get used to: Greek articles and nouns change form depending on grammatical function.

It is a very natural expression and can definitely be understood as a job title or role description. Depending on context, it could mean:

• floor supervisor
• floor manager
• person responsible for the floor
• floor warden

So yes, it behaves a lot like a set phrase, even though grammatically it is built in a normal way:
υπεύθυνος + genitive noun

Greek often forms titles like this.

A rough pronunciation guide is:

• Ο υπεύθυνος ορόφου εκκενώνει τον όροφο
• o i-PEF-thi-nos o-RO-fou ek-ke-NO-ni ton O-ro-fo

A few useful notes:

• υ here sounds like i
• εύ is pronounced roughly like ef before certain consonants, so υπεύθυνος sounds like ipefthinos
• γκ/κκ/εκκ can create a stronger k sound in words like εκκενώνει
• stress matters: υπεύθυνος, ορόφου, εκκενώνει, όροφο

If you want, you can think of it approximately as:

• o ipefthinos orofou ekkenoni ton orofo

όροφος means a storey/floor of a building, as in:

• first floor
• second floor
• upper floor

It does not usually mean the physical floor surface you walk on. For that, Greek commonly uses:

• πάτωμα = floor surface

So in this sentence, όροφος is exactly the right word because it refers to a level of a building being evacuated.

Yes. Greek present tense often covers both ideas that English separates:

• evacuates
• is evacuating

Which one sounds better depends on context.

So εκκενώνει could mean:

• The floor supervisor evacuates the floor or
• The floor supervisor is evacuating the floor

Greek does not need a separate be + -ing form the way English does.

Because Greek normally uses the definite article with a specific noun, much more often than English does.

Here ο υπεύθυνος means:

• the person in charge
• the supervisor

Greek likes to say the where English may sometimes omit it in titles or labels. In a full sentence, using the article here is completely normal and expected.

Yes, Greek often omits subject pronouns like he or she, because the verb ending already gives person and number.

However, in this sentence the subject is not just a pronoun; it is a full noun phrase:

• Ο υπεύθυνος ορόφου

So it is included because the speaker wants to identify exactly who is doing the action.
If the context already made that clear, Greek could later say simply:

• Εκκενώνει τον όροφο.
• He/She is evacuating the floor.

The subject pronoun is still not needed.