Όταν έχει συννεφιά, προτιμώ να περπατάω σε δρόμο που να είναι ήσυχος και σκιερός.

It can be understood as either, depending on how you translate it into natural English.

In this sentence, the idea is general/habitual, not one single event, so Όταν έχει συννεφιά is very close to when it’s cloudy or whenever it’s cloudy.

Greek often uses έχει + noun for weather conditions.

So:

• έχει συννεφιά = it’s cloudy
• έχει ήλιο = it’s sunny
• έχει ζέστη = it’s hot

Literally, έχει συννεφιά is something like there is cloudiness, but in normal English we translate it as it’s cloudy.

You can also say ο καιρός είναι συννεφιασμένος, but έχει συννεφιά is very common and natural.

In Modern Greek, English-style infinitives like to walk are usually replaced by να + a verb form.

So:

• προτιμώ να περπατάω = I prefer to walk

This is a very common pattern:

• θέλω να πάω = I want to go
• μπορώ να έρθω = I can come
• προτιμώ να μείνω = I prefer to stay

So after προτιμώ, να is exactly what you expect.

This is about aspect, which is very important in Greek.

• περπατάω = imperfective aspect
• περπατήσω = perfective aspect

Here, the speaker is talking about a general preference or an activity in progress, not one single completed walk. That is why να περπατάω sounds natural.

Very roughly:

• προτιμώ να περπατάω = I prefer walking / I prefer to be walking
• προτιμώ να περπατήσω = I prefer to take a walk / I’d prefer to walk once

So the imperfective fits the habitual meaning better.

They mean the same thing: to walk.

The difference is mostly style and form:

• περπατάω is very common in everyday speech
• περπατώ is also correct, but can sound a little more formal or compressed

So να περπατάω and να περπατώ are both possible. In conversation, many speakers would naturally use περπατάω.

Because the sentence is talking about a road/street in a general sense, not a specific one.

So:

• σε δρόμο = on/in a road or street, generically
• σε έναν δρόμο = on a certain road/street, but not specifically identified
• στον δρόμο = on the specific road/street

Here the meaning is more like I prefer to walk on a quiet, shady street, meaning the kind of street I like, so the article is not necessary.

This is one of the most important things in the sentence.

που να είναι is used here because the speaker is talking about a desired or suitable characteristic, not simply describing a specific road already known to exist.

So:

• σε δρόμο που να είναι ήσυχος και σκιερός = on a road/street that is quiet and shady, the kind I would want
• σε δρόμο που είναι ήσυχος και σκιερός = on a road/street that is quiet and shady, as a fact

The version with που να είναι often appears after ideas like:

• wanting
• preferring
• looking for
• needing

For example:

• Ψάχνω ένα σπίτι που να είναι μεγάλο. = I’m looking for a house that is big.

It gives the idea of a house that would be big / that meets that condition.

Because after να είναι, they are predicate adjectives, and they agree with the understood subject δρόμος.

Even though the noun appears earlier as δρόμο after σε, inside the clause the idea is:

• ο δρόμος να είναι ήσυχος και σκιερός

So the adjectives are in the masculine singular nominative form:

• ήσυχος
• σκιερός

Compare these two patterns:

• σε ήσυχο και σκιερό δρόμο = directly before the noun, so the adjectives match δρόμο
• σε δρόμο που να είναι ήσυχος και σκιερός = after είναι, so the adjectives match the subject form δρόμος

This is a subtle but very common Greek pattern.

It can mean either, depending on context.

δρόμος is a flexible word that can mean:

• street
• road
• sometimes more generally way

In this sentence, English might naturally use street if you imagine an urban setting, or road if the context is more general. Both are possible.