Extreme water damage/total roof tearoff- ok or runaway?

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I've been looking at a property that is currently for sale in a nice little pocket in Indianapolis. Several very nice homes in this area and it is a quiet area. I'm still very much a newbie and wanted to get some opinions on whether or not you would even consider a property that will most likely need an entire roof tearoff and possibly trusses replaced. 

The home is a 1900sqft brick ranch 3/2 with a nice layout but it has been neglected long enough that there is definite water damage. Looks like a small skylight where there should be just roof. The brick walls and foundation all appear to be in good shape as long as the roof is repaired sooner than later. May need some floor joists repaired though from the water logged carpets that are sinking the floors between each joist. 

My realtor has given me comps in the 150k area for ARV with possible purchase price near 20k. Thoughts on how to proceed? Looking for rehab estimates now, but wondering if i'm being too risky for my first flip. Would love to get some opinions from other BP members. Thanks!