For MacBook users, which software do you think you will use to create your UML diagram instead of NClass?
Try to use EdrawMax, it is an alternative for NClass and it might also be more compatible for Mac users.
Sounds good, are you currently using it and is it easy to manipulate?
There's also Star UML, which is free for non-commercial use and has versions for Linux and Mac!
If you are looking to do the homework we can also hand draw it. Which I think would be easier.