Forgot to post as VANITY. Sorry.
Keep in mind that this debt will be reported as yours in all future credit reports. With the amount of down payment mentioned and credit score, he should be able to get a mortgage, just not the cheapest one out there. If you are committed to help, I suggest that you be put on the title as well as the loan. That way you will have leverage should he ever default. Insist that he refinance after his credit is good and simply abandon your interest in the property. Otherwise the lender may have a claim against you or your estate at some point in the future.
Most mortgage companies do not allow co-signing because Fannie Mae and Freddie Mac will not buy the loans. You would have to go on as a co-mortgagor. That means you would own 50% of the house, be on the title and fully liable for the mortgage if your relative defaults.
In addition to the above liabilities the full amount of the mortgage payment would be used agains’t you in calculating your qualification for a new mortgage if you decide to sell your current home and buy another or purchase a second home or an investment property.
From what you have told me your relative is possibly not ready to be a homeowner quite yet. Over my 27 years in the mortgage industry I have counseled many people to pay off all of your delinquent credit and get your scores up before you attempt to purchase a house. Some listen, some don’t, some talk their relatives into helping them.
I give this advice to you as a 27 year veteran of the mortgage industry both as a mortgage loan underwriter and a mortgage broker.