What is a physical description of Miss Maudie? Where does it occur in To Kill a Mockingbird?

The lengthiest semblance of a physical description of Miss Maudie is found in chapter sixteen, when Scout makes the following observation:

There was an odd thing about Miss Maudie—on her porch she was too far away for us to see her features clearly, but we could always catch her mood by the way she stood. She was now standing arms akimbo, her shoulders drooping a little, her head cocked to one side, her glasses winking in the sunlight.

Most of what we learn about Miss Maudie has to be searched for throughout the text. Other descriptions state that she was "a chameleon lady," suggesting that she changed her attire to suit the circumstances. As Scout comments in chapter 5:

She was a widow, a chameleon lady who worked in her flower beds in an old straw hat and men’s coveralls, but after her five o’clock bath she would appear on the porch and reign over the street in magisterial beauty.

This suggests that her transformation from the one to the other was quite dramatic. Scout also mentions that Miss Maudie's "speech was crisp for a Maycomb County inhabitant," which might imply that she did not entirely use the local vernacular and sounded more cultured. She also wore dentures since she, at one point, "thrust out her bridgework" making Scout like her even more. Scout admired the two small gold prongs clipped to her eyeteeth that Miss Maudie displayed whenever she grinned, which led to her revealing her false teeth. Because of her dentures, Miss Maudie could also not chew gum.

Miss Maudie also seemed to have quite a stern, authoritarian voice, for Scout also states that "Miss Maudie’s voice was enough to shut anybody up." It is also clear that she has a well-endowed buttocks because when Scout was aiming to shoot her and Atticus asked her what she was aiming at, she said: “Miss Maudie’s rear end.” We are then informed that Atticus turned and saw Scout's "generous target bending over her bushes."

We can also assume that Miss Maudie is fifty years old because she does, at some point, mention that fifty is not too old when she and Scout discuss Maycomb's history and age and she indirectly refers to herself. 

Miss Maudie is a pleasant, open-minded woman who clearly loves children and the outdoors. She has endeared herself to both Jem and Scout for her kindness and objectivity.