I'm a last year undergraduate student and I have taken a graduate course in geometric group theory.

I'd like to start reading some more advanced stuff in geometric group theory and in particular about automorphisms of free groups. (In specific I'm interested in $\operatorname{Out}(F_n)$.)

Could you please suggest me material (books, notes, papers)? I've started studying "The topology of $\mathrm{Out}(F_n)$" by Mladen Bestvina. Are there any similar works (or more introductory ones)?

If this is not the place for such a question please let me know.