The best chest-builder is the bench press but to target the upper chest you need to do the
Incline Bench Press, Incline Dumbbell Press, Incline Dumbbell Flies but if you cant do the Incline then do the Reverse-Grip Bench Press which has been proven to target the upper chest more than the Incline. You can also do Decline Push-ups.
Your pecs are your chest so just do the Bench Press and Flies and Push-Ups.
The man above me was right, the bench press also includes some help from the shoulders but it isnt the best exercise for it. You should do the Shoulder Press, the Military Press, Front Shoulder Raise, and Lateral Shoulder Raise.
Also have a high protein diet, pack on calories.