Roofing magnate—and the richest self-made woman in America—Diane Hendricks is No. 8 with $11 billion from her nearly 40-year-old company, ABC Supply.

Only 56 women made this year’s Forbes 400 list of the richest people in America—but as a group they’re wealthier than ever. The women on the Forbes 400 are worth a combined $452 billion ...