So I made a deal, sight unseen, over the phone. We negotiated price after a few calls. Here was my thinking...I can do quite a bit of research via public record and doing driveby of the property. Then I simply asked the seller...what does the property need in terms of maintenance/repairs and updating?  In this case, the seller said it will need a roof in the near future and its otherwise ready to go. 

Today I did an unofficial inspection and am still waiting on the professional inspection to be done. I think it will roughly cost 17k to get the duplex in shape. Im accounting for 5k for the roof, so thats about 12k that I wasn't told about. We negotiated a solid price, 65% LTV pp. this will bring it up to 73% LTV pp, still not a bad deal.

How do I go about renegotiating if the inspection comes back like i think it will?

@Reggie Maggard

share your report to ask for a reduction. However, keep in mind if the seller is not motivated to sell they might walk away.

Maybe you can throw them a bone that doesn't cost you much, say moving the closing dates. If they agree to a reduction.