Do you know what your challenges are? I ask because many Buyers make assumptions, thereby disqualifying "themselves." Unless you have made application and have been declined, I strongly suggest you speak with a lender. If you have been declined, you should have a reason and from there given ways to improve whatever the problem may be.
Answering your question...If a lender won't touch you, there are only two options - cash or seller financing. If doing seller financing, make sure the terms are in line with what you can afford. The last thing you want to do is strap a bomb to your chest! All means considered ("means" you will investigate) it may be best to wait until you can qualify for a loan of your own.
Good luck, and please be "very" careful should you choose seller financing!