Determining cost/damage of water before making offer?

[Roshan Taheri]

I went to look at a property this morning that is owned by a close friend of mine. He seems to have neglected the property for the last 7 years and is looking to get out of the real estate business. The gutters haven't been cleaned in 5 years, so there's one gutter that has detached from the house in the front, and the overflow has rotten the deck in the back. In the attic, the water looks to have gotten through the siding onto the flashing and basically it crumbled/fell onto the attic floor after being saturated...but the siding is still there, but there's just no foil flashing. There's no indication of water damage inside the house/ceiling, but I'm worried about damage that an untrained eye can't see...like wooden beams rotting.

I'm trying to figure out how to go about estimating the cost so that I can make an offer on the property, but I don't really know what the extent of the damage is without having a professional take a look. Who would you recommend that I hire to consult/take a look at something like this before going and making an offer? My friend is worried that if I hire someone to go take a look and he finds something...and I don't buy the property, he'd have to disclose it to anyone who comes along and wants to buy it as-is? Is that true?

Could really use some advice on this one...and maybe that advice is to stay away and let someone who is more experienced take on the deal, which is fine, but I'm looking for any guidance that I can get.