Owning your own home

Wasn't the new roof predicated on Google telling you that clay tiles last somewhere between 50 and 100 years?

And the house is comfortably the cheapest on the street already?... could deduct the potential costs from the most expensive house on the street, and then if the one you're looking at is still cheaper than that then you're probably at a decent place

4.5k sounds cheap tbh. I think we payed nearly 10 for the roof on our old place when it was replaced 10 years ago (valley roof on a Victorian terrace)

im not sure 4.5k is realistic, maybe for just materials?

we had a new roof, we took the cheapest quote which was 12k with the highest being 25k (2 bed up and over terrace roof)

If you try and chip them for £4.5k because you think it might need a new roof and that hasn't been brought up in the survey or there is no visible sign of damp or leaks, then I'm afraid you're contributing to the worst parts of buying/selling. The sellers likely haven't replaced it as they don't think it needs it. If it is not leaking/visibly sagging/tiles coming off left right and centre or the surveyor hasn't said "not sure about roof but will likely need replaced in 5-10 years, then the seller would be totally reasonable to tell you to jog on.

And using "they need my purchase to get their dream home" is pretty shitty tbh.

If it doesn't need replaced now, it will in future. Maybe by you, maybe by the next owner. But that is part and parcel of owning a house. You don't negotiate based on every potential future expense. If something is falling apart now and the place hasn't been priced accordingly, then go for it. But if surveyor and lender agree the house is worth the accepted offer, then caveat emptor.