После ремонта старый чердак превращается в небольшую мастерскую.

Because the preposition после always takes the genitive in Russian.

• после ремонта = after the repair / after the renovation
• Base form: ремонт
• Genitive singular: ремонта

This is a fixed pattern:

• после урока = after the lesson
• после работы = after work
• после дождя = after the rain

So после ремонта is grammatically required.

Because it is the subject of the sentence — the thing that is undergoing the change.

• старый чердак = the old attic
• It is what turns into something else.

In Russian, the subject is normally in the nominative case.

Here:

• старый is nominative masculine singular
• чердак is nominative masculine singular

So the sentence structure is basically:

After the renovation, the old attic turns into a small workshop.

Превращается means turns into, becomes, or is transformed into.

It comes from the verb превращаться.

This verb often suggests a real transformation from one state into another, stronger than simple becomes in some contexts.

For example:

• гусеница превращается в бабочку = the caterpillar turns into a butterfly
• комната превращается в офис = the room turns into an office

So in your sentence, the attic is not just being described differently — it is being converted or transformed into a workshop.

The -ся is part of the verb превращаться. In this case, it does not literally mean that the attic is doing something to itself in the English sense.

Russian -ся verbs can have several functions. Here it helps form a verb meaning something like:

• to turn into
• to be transformed into

So превращать and превращаться are related, but different:

• превращать что-то во что-то = to turn something into something
• превращаться во что-то = to turn into something

Compare:

• Они превращают чердак в мастерскую. = They turn the attic into a workshop.
• Чердак превращается в мастерскую. = The attic turns into a workshop.

Russian often uses the present tense imperfective to describe:

• a current process,
• a repeated pattern,
• or a general fact / narrative present.

Here превращается suggests a process or result viewed as something happening as part of the renovation context:

• is turning into
• becomes
• is being transformed into

If you wanted a clearer one-time future result, Russian would more likely use the perfective future:

• превратится = will turn into / will become

So:

• чердак превращается в мастерскую = the attic is turning into a workshop / becomes a workshop
• чердак превратится в мастерскую = the attic will turn into a workshop

Because the expression превращаться в + accusative means to turn into something.

So after превращаться, Russian commonly uses:

• в + accusative

Here:

• мастерская is the dictionary form
• accusative singular: мастерскую
• adjective небольшая becomes небольшую to agree with it

So:

• в небольшую мастерскую = into a small workshop

This is a very common pattern:

• превращаться в проблему = to turn into a problem
• превращаться в музей = to turn into a museum
• превращаться в привычку = to turn into a habit

Because it agrees with мастерскую, which is:

• feminine
• singular
• accusative

The adjective must match the noun in gender, number, and case.

Dictionary forms:

• небольшой = small
• мастерская = workshop

In this sentence:

• в небольшую мастерскую

Both words are in the feminine accusative singular form.

A quick pattern:

• nominative: небольшая мастерская
• accusative: небольшую мастерскую

Yes, мастерская usually means workshop, studio, or workroom, depending on context.

It can refer to:

• an artisan’s workshop
• an artist’s studio
• a place where things are made or repaired

So небольшая мастерская could be:

• a small workshop
• a small studio
• a small workroom

In your sentence, workshop is probably the most natural translation.

Both can sometimes be translated as becomes, but they are not identical.

• становится = becomes
• превращается = turns into / is transformed into

Превращается usually emphasizes a stronger change or transformation.

Compare:

• Комната становится тихой. = The room becomes quiet.
  This is just a change of state.
• Комната превращается в спальню. = The room turns into a bedroom.
  This is a transformation into a new function or identity.

Since an attic is being converted into a workshop, превращается is a very natural choice.

Yes. Russian word order is more flexible than English, although the original sentence is very natural.

Original:

• После ремонта старый чердак превращается в небольшую мастерскую.

Possible variations:

• Старый чердак после ремонта превращается в небольшую мастерскую.
• В небольшую мастерскую после ремонта превращается старый чердак.

These versions are all grammatically possible, but they shift the emphasis.

• Starting with После ремонта highlights the time/context.
• Starting with Старый чердак highlights the subject.
• Starting with В небольшую мастерскую emphasizes the result.

The original version sounds neutral and smooth.

Превращается is imperfective.

Its perfective partner is превратиться.

So the pair is:

• превращаться = imperfective
• превратиться = perfective

Use them like this:

• Чердак превращается в мастерскую.
  The attic is turning into / becomes a workshop.
  Focus on the process or general description.

• Чердак превратился в мастерскую.
  The attic turned into a workshop.
  Focus on the completed result.

This is a very common Russian aspect distinction:

• imperfective = process, repetition, general description
• perfective = completed event, result

A natural stress pattern would be something like:

После ремо́нта ста́рый черда́к превраща́ется в небольщу́ю мастерску́ю.

Main word stresses:

• после
• ремо́нта
• ста́рый
• черда́к
• превраща́ется
• небольщу́ю
• мастерску́ю

The sentence stress in actual speech would often fall especially on the newer or more important information, often near:

• чердак
• превращается
• мастерскую

So a speaker might naturally emphasize the transformation: После ремо́нта ста́рый черда́к превраща́ется в небольшу́ю мастерску́ю.