Any good dumbbell workouts to build lats up

Just high rep heavy weight dumbell rows with loose form.

 

DB rows
DB bentover rows
DB Supermans (if you are capable)

As fa as pull-ups, I recommned the Lebert Equalizers. You can do dips, push ups, Inverted Rows (alernatives to pull ups), etc...

Probaly the best equipment I have ever used next to my Olympic Bar and heavybag

 

High repetition exercises, heavy or not, are generally for muscle endurance & conditioning purposes. If he is trying to build his lats up (I am under the idea that he wants strength and size) he should be focusing on low rep/heavyweight exercises.

Not trying too bust your chops though

 

The Iron Gym pull-up bar hangs on the door frame and comes down completely so you can shut the door. Only costs about 20 bucks. However, it's tough to get a good wide grip on door mounted bars.

Grabbing one's wife by the ankles and swinging her around like an indian club is a real lat builder.