What problems do American Bulldogs have?

My friend has a relative that breeds American Bulldogs, she said I could have a puppy for free and I'm just curious If there is anything I should know before I make a commitment that I might be in over my head for. I really want this puppy and I'm pretty sure I would do anything for it. I'm not able to talk to my friends cousin because well we aren't friends and my friend always forgets to ask him questions that I have. Help? Anyone with experience, advice?