Steroids don't build muscles, what they do is boost or facilitate the rate at which you can build muscles. If you really need natural muscles then specialise in certain kind of exercises. For Instance carrying the balancing weighs several times a day everyday. Doing the exercises plus taking the steroids can really make you get muscles fast.
But then, you need to be aware that steroids also have side effects. For instance, it can lead to imbalancement of body structure/shape. You'll find that one part of the body is bigger than the other especially the upper part of the body. Not this alone but you'll realise that steroids also have other body effects and can really affect you if you use too much of them. The most crucial thing is balancing between steroids and exercises.