If you are wanting to buy something big you should save enough money to buy it straightforward instead of getting a nice car and making large payments or getting a cosigner. Having a co signer could turn out bad because you may have someone buy you a car and turn around and take it away all because of some stupid mistake like not paying them one payment. Then you would be carless.
More examples why you should just make your own full purchases instead of relying on other people would range in a lot of ways. Buying your own things could make you feel better when it comes down to it. You will feel more responsible if you pay the full payment for large purchases that you wan. If you let someone else buy you