Home Depot and Lowes both offer "project financing" for major projects - their credit underwiting is not too difficult, however sub-600 scores might be an issue -talk to them in a store and see how it goes since they'll know you are standing there offering a profit based sale. I give you a 50/50 shot with your score, you might get lucky.
Note that I used a Lowes "project finance" at just under $10k for a roof at 84 months 4.99% a few years ago - paid it off in 36 months and I think the APR is higher now.
Edit/Add: You might be able to get away with a patched or repaired roof as a short term fix, years ago I had water running down my brick chimney inside, turned out just to be the flashing - couple hundred bucks - our roof was 26 years old before it had to be redone..
