How to buy a gas station business?

A friend of mine wants to put up a small gas station here in Texas. He wants that kind of business because there is only a little gas station business running in our town. He asked for my help and I am willing to help him. We found a good commercial lot in town and we like the place where the gas station will be put up. I need to know on what is the best thing to do, Franchise or buy our build our own gas station. How to buy a gas station business?