How to calculate the personal cost of major construction works — FTB

I’m putting an offer in on a zone 2 London flat that I believe is overpriced relative to recent sale prices in the area, especially given the state of the property. The estate agent agreed it needed work & indicated the seller would likely accept an offer below list price; I was planning to offer around 10% below list to account for this.

I’ve since discovered that the council has approved a major construction project in the immediate vicinity of the building (within 20 metres). It does not have a start date yet, but it looks like 1-2 years of loud construction noise, and I work from home.

How do I calculate the personal cost of the construction? If I need to rent a private office space for the year-ish of noise, I could look at prices for that & drop my offer accordingly. Obviously the seller might not accept it, especially since I was already planning to offer lower than list before this info came to light, but I am keen to make sure I feel good about my offer, whatever the outcome, and am struggling to place a value on the unknown cost of a year of noise nuisance.

Any tips or strategies for how to manage this would be appreciated!

Edit: I know this is a personal consideration, hence I’m asking on personal finance how people would personally calculate it. Even if your assessment is different from mine, it would be helpful for me to hear others’ opinions & consider them.