Buy it. Cash. Now! Figure out the rest later.
Echo the other points above and figure out what your goals are as far as keeping it for a rental, or selling it quickly. Only you can answer that.
As far as the rest, with minimal holding costs (no mortgage!), you have the luxury of taking your time in the rehab. Here are a couple options, in no particular order:
1. take out a personal/home equity loan. Usually around 10% interest, depending on your credit.
2. use a credit card. higher interest, and harder to pay contractors.
3. Get a Home Depot/Lowes card and use them for as much as possible, taking advantage of the no interest financing for 6-24 months. They'll do roofs, flooring, HVAC, appliances, cabinets, windows...etc. Credit score and income will dictate the limit on the card.
4. Refi immediately. They may be more apt to lend you money if you already own the property, but then you'd have to pay closing costs, which may be more than the financing costs associated with a credit card or personal loan.
5. stretch the repairs out over a period of time and DIY, paying cash along the way.
6. any combination of the above.
Again, only you can determine which is the best option for you, depending on your situation.