Looking for advice and potentially a partner

[Brian Chase]

I have a lead on an off-market deal in downtown Tucson. It is a duplex in really bad shape about a mile outside of downtown (but still in 85701). It's about a 0.23-acre lot zoned R-2. I previously looked at the property with a contractor whose advice was to just knock down the structure and start over. There were roof leaks, mold, needs all new appliances, flooring, etc. I didn't purchase at the time and the owner put the property on the market, but no one bought it and he took it off the market. He just reached out to me again to see if I was interested. 

I am very interested in this property for a number of reasons, but I'm not sure how to evaluate it. I don't know how to estimate construction costs if we were to do a complete teardown and start over. I also don't have any connections to contractors. The guy I had worked with before switch jobs. This would be my first investment, so it is a bit daunting to start with such a big project. On the other hand, I think there is some great potential. 

I'd love to hear what you all think. What questions should I be asking? Is there a good way to go about figuring out construction costs?