Is this sentence gramatically correct?

Yes. It’s a little awkward but I think it’s grammatically correct.

It is awkward. You can make it less wordy by saying, “Won’t you repair the roof before winter sets in?”
But the part in bold seems to be correct.

Grammatically correct but wordy. How about “Don’t you need to repair the roof before winter sets in?”

Oops I forgot to mention..
Somehow the word have must be used..

Then add have to @janbb‘s example:

“Don’t you need to have the roof repaired before winter sets in?”

I think it’s correct. Those who want to change it leave out the meaning of necessity. Imagine the sentence is a response to “Oh, my roof needs repair and I can’t afford it.”

“Don’t you have to repair the roof before winter sets is?”

It is correct, and it is what many Americans would say.

Hey, we say this in the south all the time, so its got to be correct.

Will you have to repair your roof this fall?

Nine words.

Aren’t you going to have to repair the roof before winter sets in?”

How about: Won’t you have to… or Don’t you have to… or You might have to…

Try this in a loud voice…GET THE DAMN ROOF FIXED NOW!!

You didn’t use “have”.

Do I have to beat your ass? Fix the roof already!

It’s correct; it just sounds odd said slowly when most people would say “gonna hafta repair”.

There’s nothing wrong with it. It sounds like normal conversational English to me. To the people who are saying it’s “wordy”: why do we need to conserve words?

“Fix the effing roof.”
Four words.

It’s February. The roof should have been fixed already.

Yes, it’s correct, and there’s nothing wrong with it at all. It’s perfectly clear.

I would not use “need,” which (despite its now-common use in this sense) has a different meaning from “have to.” “Have to” means “must” and is not about need. It’s about obligation or requirement.

As long as we’re not paying a metered rate for word usage, I favor clarity over frugality.

I agree with @Jeruba. If I were going to try to shorten it, or make it slightly more straightforward, I would say,

“Won’t you have to repair the roof before winter sets in?”

This implies that you’re talking about this winter, whereas “Don’t you…” implies every winter.

Does it have to be asked in the negative?

Are you going to have to repair the roof before winter?

Do you have to repair the roof before winter?

Aw, JLeslie, don’t be negative towards the negative – it’s already so downtrodden. :)

@dappled_leaves One of my English profs used to accuse me of getting right to the point. She said I would be good at business writing, eliminating dead wood, she wished I used more transitions. She said I write like everything is in bullet format. Haha.

You could use the modal verb would. Would you know it? The roof still aint fixed.

Sorry, @Gagan107; “Aren’t you going to have to repair the roof before winter sets in” is perfectly acceptable, if a bit wordy.

“Are you not going to…” is also correct but sounds very stiff. No native speaker would normally say that excpt perhaps for emphasis. A more informal version would be, “You’re not going to repair the roof…?” Unspoken is “Why ever not? Are you an idiot. What about leaks?”

If anyone wants to be persnickety about not ending a sentence with a preposition, they could also suggest:

Are you not going to repair the roof before in sets winter?
or
Won’t you repair the roof before the onset of winter?
or
Ain’tcha gonna fix yer roof afore winter?
or
Da’ fuck, man, fix y’damn roof already!

Are you not going to repair the roof before in sets winter??

Persnickety oy vey.