tuìfáng yǐqián qǐng gěi wǒ fāpiào.

In Chinese, time expressions like 以前 often come after the event they refer to.

So:

• 退房以前 = before checking out
• literally: checkout + before

This is a very common pattern:

• 吃饭以前 = before eating
• 上课以前 = before class / before attending class
• 睡觉以前 = before sleeping

So even though English says before checkout, Chinese naturally says checkout before.

Yes. All three can mean before checking out:

• 退房前
• 退房之前
• 退房以前

For many everyday situations, they are very similar.

A few notes:

• 前 is short and very common.
• 之前 sounds a little more explicit and is extremely common in spoken and written Chinese.
• 以前 also works, but depending on context it can sometimes mean formerly / in the past, so beginners often find 之前 easier to interpret.

In this sentence, all of these are acceptable:

• 退房前请给我发票。
• 退房之前请给我发票。
• 退房以前请给我发票。

Here, 退房 means to check out of a hotel room.

Literally:

• 退 = return / withdraw / check out
• 房 = room

So in a hotel context, 退房 is the normal way to say check out.

A related word is:

• 入住 = check in

So:

• 入住时间 = check-in time
• 退房时间 = check-out time

Yes, 请 here is used to make the request polite, similar to please.

So:

• 请给我发票 = Please give me the invoice/receipt

In Chinese, 请 often goes before the verb phrase you want someone to do:

• 请坐。 = Please sit.
• 请等一下。 = Please wait a moment.
• 请告诉我。 = Please tell me.

It is polite, but not overly formal.

Because 给 here introduces the person who receives the thing.

Structure:

• 请 + 给 + 我 + 发票
• please + give + me + invoice

So 给我 means to me or give me.

This word order is normal in Chinese:

• 给我菜单。 = Give me the menu.
• 给我电话。 = Give me your phone number / call me, depending on context
• 给我发票。 = Give me the invoice/receipt

So 我 comes before 发票 because it is the indirect object: the person receiving the item.

That is a very good question. In real-life Mandarin, 开发票 is often more natural when you mean issue me an invoice / receipt.

So in a hotel, many people would say:

• 退房前请给我开发票。
• 退房之前请帮我开发票。

Why? Because 开 in 开发票 means to issue/write out an invoice.

By contrast:

• 给我发票 can sound like give me the invoice
• 给我开发票 more clearly means issue an invoice for me

So your sentence is understandable, but 给我开发票 is often more idiomatic in this situation.

It can be translated as receipt in many learner materials, but 发票 is more specifically an official invoice.

In mainland China, 发票 is an important official tax document. It is often what people ask for when they need proof of payment for reimbursement or business records.

This is different from 收据:

• 发票 = official invoice / tax receipt
• 收据 = a more general receipt

So at a hotel, restaurant, or company, if you need the official document, 发票 is the right word.

Chinese often leaves out the subject when it is obvious from context.

In this case, the speaker is talking to hotel staff, so the understood meaning is:

• (You/the hotel staff), please give me the invoice before I check out.

Chinese does this a lot in requests and conversations:

• 请等一下。 = Please wait a moment.
• 请帮我一下。 = Please help me a bit.
• 请给我菜单。 = Please give me the menu.

The subject is omitted because everyone already knows who is being addressed.

It is not required here.

You can say:

• 退房以前请给我发票。

You can also say:

• 在退房以前，请给我发票。

Adding 在 makes the time phrase more explicitly marked, but both are grammatical.

Compare:

• 吃饭以前洗手。 = Wash your hands before eating.
• 在吃饭以前洗手。 = Wash your hands before eating.

Both are fine. The version without 在 is often more concise.

Yes, it is polite enough, especially because of 请.

If you want to sound a little softer or more natural in customer-service situations, you could say:

• 退房前请给我开发票。
• 退房前麻烦给我开发票。
• 我退房前想开发票。
• 麻烦您在退房前给我开发票。

Notes:

• 麻烦 makes the request softer, like could you please...
• 您 is a polite form of you
• 想 can make the request feel less direct

So your original sentence is polite, but there are even more natural customer-service versions.

A helpful way to break it down is:

• 退房以前 = before checking out
• 请 = please
• 给我发票 = give me the invoice / receipt

So the structure is:

time phrase + polite marker + verb phrase

This is very common in Chinese:

• 明天请给我打电话。 = Please call me tomorrow.
• 回家以前请关灯。 = Please turn off the lights before going home.
• 吃饭以后请洗碗。 = Please wash the dishes after eating.

So the sentence follows a very normal Chinese pattern: when + please + action.