Whenever I get asked by young guys about how to make their chest bigger, I always say, "Do more rows"! To which they always look at me let I have two heads!
Let me explain here. If you have poor posture like the picture below more bench pressing, or any horizontal pushing will only do you more harm than good, and give you a smaller looking Pec area, rather than the barrel chest look you desire.
In the picture above my posture is so bad, that you cannot even see my chest. If I was to do more bench pressing, or any type of horizontal pushing it would actually make me chest look smaller NOT bigger, by pulling me more into this dysfuctional posture. Now if I was to strengthen my upper back, and get my shoulder blades back, my chest would look like it just magically grew tenfold! See in the picture below
Good Posture from some upper back work
Also if you have poor posture like in the first picture, the function of shoulder into overhead positions is going to be greatly comprised. Look below.
Alter overhead mechanics due to poor posture
In the picture above there would be no way in hell you would let someone with this overhead movement pattern press a weight overhead. Now if you wanted to really get optimal hypertrophy of your shoulders, you would want to press overhead. But you could not run the risk of pressing overhead with the posture in the picture above.
Now if again I was to strengthen my upper back, and work on some other things (like t-spine mobility and proper breathing patterns from the diaphragm), I would put myself in a much better and safer position to overhead press. In the picture below, you can see that my upward rotation of my scapula is far better, safer, and more efficent with good posture. This effectively will allow me to overhead press without any compensation, while keeping my shoulder healthly in the long-term also.
Optimal Overhead Positional due to better posture
Show there you have it. It you want a bigger chest and shoulders, DO MORE ROWS!!