Wide grip pull-ups x4 6-10 (These are much better than lat pull downs,they add thickness and width) Add weight when you can do 12 bodyweight reps.
Deadlifts x3 6-10 (use good form or you will snap up your lower back)
Bent over rows x3 6-10 (this really adds thickness to your middle back)
One arm dumbbell rows x3 8-12
This sample back workout is guaranteed to build a aesthetic back in conjunction with a good diet.