You can have the major problems fixed by the seller
You can pay for them as the buyer
You can and the seller can split the costs.
The other option is rather than just repairing the roof; you could have a new roof installed if the current one is too old or the condition isn’t very good. That is where having an excellent real estate agent comes in handy. The outstanding ones know how to negotiate while keeping the sale moving along, and all parties involved happy.