[squiffy]

A lot of sellers want to sell as is. Few sellers want to take the time and effort to fix up their place.

It's especially risky for a seller to spend 10K on a new roof that you may or may not like or that you may or may not approve.

I really side with the seller on this one. Unless I were really desperate, if I were a seller, the last thing I would want to do is have a sale contingent on your liking the quality or price of the new roof.

If you want a new roof, you should put it on yourself. If you think the home is only worth x with an old roof. Just offer x, what you think it's worth with the old roof.

This isn't some fancy Texas hold em hand in the final round of the World Championships. You don't get style points for degree of difficulty. Bet for value.

I cannot imagine why you would want to make a new roof part of the negotiations. It's only going to complicate things.

Offer him what you think the home is worth, then walk away. If you get it. Then spend the 10K to put your own roof on.
I really disagree with how you are looking at this, particularly at the issue of the roof.

When negotiating for a huge purchase like this, you need to keep things simple.

A lot can go wrong if he hires a roofer and the roofer does a lousy job. All the risk is on him. Plus he cannot predict if you will be reasonable and approve the roof, or be unreasonable and reject it based on some idiotic objection.