Unreasonable to renegotiate after a survey?

[foursquares]

Property originally listed last year (2025) for £520k. Reduced to £475k, didn't sell. On market for 6 months.

Reslisted this year for £450k. One offer in first week, no other offers apart from mine (accepted £435k in 4th month).

I've had a building survey done and needs a new roof (costs £20k approx from roofer and other £5k works).

Seller not budging on price, as he think he's already reduced significantly, so Aibu to expect negotiation on price?

But this is only if you can afford a new roof if the house price wasn’t hiked up.
We can’t afford a new roof as we’re already paying top price for this house, without roof issues.
If the sellers haven’t maintained it at all over all their years, why do they feel it would be the buyers responsibility to take it on?

I am genuinely asking as I feel like this kind of thing is seen in two completely different lights.

If it’s the perfect house for you and you can afford a new roof and you are going to live there for sometime, it can make sense.
When you come to sell it, you won’t need to give a discount for roof repairs and it’s more salable than one without a new roof.

There are not many decent houses out there.
I fully agree that owners who don’t maintain their properties (my FiL for instance) shouldn’t expect top dollar, but it’s not a perfect world.