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For a basic 3-day mass routine I would do the following:
Monday (Back/Biceps):
Deadlift
Chin-Up or Lat-Pulldowns
Bent-over Rows or T-Bar Rows
Bicep Curls
Wednesday (Chest/Triceps/Shoulders):
Flat Bench Press or Weighted Dips
Incline DB Press
Tricep Dips or Skullcrushers
Military Press
DB Shoulder Press
Friday (Legs/Abs):
Barbell Squats
Stiff Legged Deadlifts
Calf-Raises
Weighted Crunches
Your 6-8 rep range is a good one for gaining mass and your 20 minutes of cardio after weight training is a good idea as you will have already burned all of your muscle glycogen stores up training and burn fat. It is also important that you try to get your weights session done in 45-60 minutes, staying in the gym too long can have a negative effect.
Your triceps and shoulders will be used in most most pressing movements, so heavy bench press / military press should beef them up nicely, however diet is VERY important in bodybuilding and in my opinion is where you are lacking most.
The key things are:
- Try to get at least 1.5g protein per pound of bodyweight per day.
- Take whey in water upon waking and whey in dextrose post-workout. As you are doing cardio it may also be beneficial to take whey in water straight after weights, then dextrose after your cardio.
- Try to get your carbs from oats/brown rice/wholemeal bread etc, they are low GI and will sustain you much better without flucuating blood-sugar levels.
- Try to eat every 2 hours, eat little and often if you have trouble eating this regularly.
- Before bed consume a slow-release protein source food such as tuna, cottage cheese or a casein shake.
- Drink plenty of water!