My 5 year old keeps saying he wants to be a girl. He has been saying this since I can remember. He preffers girl stuf than boys stuff. Is this normal?

Normal. At 5, gender identity is not stable and continues to change as a child matures. Give it another 2-3 years!
Not common. But no longer considered "abnormal." gender identity tends to be established by 2-3 years of age. Children can have "gender variant behavior, " which refers to the child who prefers interests/activities associated with the opposite sex; or can be transgender, where they persistently feel, to the core of their being, like they should have been the opposite sex. You must discuss this with experts.