Allow me to break down the appearance of each character individually as described in Harper Lee's novel:
Calpurnia is a lean but stern-framed African-American woman. She typically dresses for her role as maid and nanny, meaning that period workclothes were her common wardrobe. However, when attending church, Calpurnia dresses up, donning dress, hat, and all the habiliments (H. Lee's word) for such an occasion.
Atticus is a taller, lean-framed intellectual. He wears glasses, normally wears a suit and tie, and speaks nearly flawless English, as is the custom for professionals of this era. When Atticus is at home, he "dresses down" or becomes more casual, as is the standard for men of this era.
Jem, depending on what point in the novel we are describing him from, is your average pre-teen southern boy: his dress and manner reflect the geography and culture of the area. Typically, he dresses in pants or short pants, the average shirt, and depending on the weather, he and Scout may run barefoot.
Scout, despite being a girl, dons clothing that denote her tomboyish nature: Rather than wearing a dress, she prefers overalls or even pants, much to the chagrin of Aunt Alexandra and the "proper" women of Maycomb County. Her hair is cut short, but not overly so. All of the Finches, including Scout, are caucasian.
In To Kill A Mockingbird, the description of each character's physical appearance is not extensive, but author Harper Lee gives certain details which help the reader to create an overall mental picture of each of the important characters.
Scout is often described as small, especially at the age of 6, fair-haired, and tends to dress boyishly. Using the time period, the family's economic status, and regional culture as guides, it can be assumed that this means she wears pants rather than skirts or dresses, and may even wear hand-me-downs from Jem.
Jem is sometimes described as tall, but usually only in relation to Scout. Quotes from the novel evidence that he has straight brown hair and that he enjoys sports, which may indicate that he has an athletic build. He tends to blush easily and has fair skin.
Atticus has graying hair that was once black, and is described as tall. He wears glasses and has trouble seeing from one eye.
Calpurnia is a thin African-American woman, described as being bony and tough. She has large hands and may have trouble seeing as well, as she often squints.