Been rewatching Doctor Who lately and adapted some of the first few characters into a cartoony style for practice. I paid close attention to the actors' facial structure and personality when designing their look.
Nine- Chris Eccleston is tall with broad shoulders, so his main shape is pretty Square to also match his up front personality.
Rose- Billie Piper's personality as Rose fit the round type of character shape since she's very compassionate, but I also considered her curvy physic when drawing her body. Ten- David Tennant's a wild card, a triangle suited him best since he's very cunning and mischievous. His skinniness was also a factor in determining his body shape.
Martha- Freema Agyeman's character was like Rose's, a compassionate round, but her outfit and wild ponytail also helps give the impression of her being very headstrong.