How to approach a bank to get purchase and rehab financing?

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There is a run down property near me in an excellent neighborhood. It was last sold in the 1980s and has holes in the roof and appears unmaintained.

A typical home in that neighborhood costs around $650k. I assume it will need 80-120k in rehab and updates. If the owner will accept an offer of 500k, then it is definitely worth it.

I'd like to approach the owner to buy it and then rehab it so I can either move in or sell it. 

The problem is that I don't have 620k in available cash or credit on hand. I have a HELOC with about 80k available that I could use as a down payment.

i have a good relationship with a local bank but I could use some advice on my approach. If possible, I'd like for a bank to finance the purchase and rehab cost. Any tips for approaching a bank with this and what I can expect from them?