Building calf muscles is one of the hardest muscles in the body to work. Why? Because the calf muscles are naturally toughened up by daily walking, an activity that is impossible to avoid! Also, the longer the calf muscle, the larger its volume and the more need to intensify the approach to building the same.
So the challenges in building up the calf muscles are totally different than the challenges in building up any other muscle in the body but is it impossible? Not at all! First of all, it is important to realize that to compensate for these challenges, training harder is not the answer, nor is cutting down on rest time between sets.
You must set up a structured regiment of sets and begin at the point where they are what you can handle and then gradually build up the number of sets as your endurance (and muscle tone) improves.
Of course, there are specific exercises geared specifically for the building of calf muscles but it is important to remember that to over-do the following and to not allow for rest time for the calf muscles between sets will only cause undue muscle strain and ultimately slow down the progress of building larger calf...