I can't write a chart in here, but I can help you get started in thinking about the content of that chart. There are really only three characters in this story, so at least that makes the task not too difficult. Let's start with Sue and Johnsy: they are both young, female, struggling artists, and seem to be kind and a bit naive and innocent. They are different in the fact that Johnsy seems a bit weaker (an impression given through her getitng ill in the first place, then deciding to die at the falling of the last leaf), Sue seems to be more realistic and practical (she works even though Johnsy is sick; she tells Johnsy to stop fixating on the leaf). Then, there is Sue and Behrman. They are similar because they are both struggling artists, they are both concerned about Johnsy, they both try to help her in their own ways, and both understand the artist's life (he comes up to pose for her painting). They are different because they are male and female, he is gruff whereas she is gentle and kind, she doesn't "think outside the box" and he does (he paints the leaf; she just tries to nurse Johnsy back to health). Then, there is Johnsy and Behrman. They are similar because they are both struggling artists, and both friends with Sue. They are different because he seems to have an enduring and brusque personality, whereas Johnsy seems more apathetic and feminine.
I hope that those thoughts help to get you started; you should be able to take them, along with your own thoughts on the matter, and fit them into a chart formation pretty easilty. Good luck!