Q: how can i build mucsle and gain some fat

A: If you don't mind or actually want some fat gain along with muscle gain, then you are in luck! All you need to do is have a good weight training program such as any of the 'Split' ones I list in my Weight training article AND a diet on which you eat enough food to slowly gain weight. If you are finding that you are not gaining weight, then you simply need to eat more! For some people it can almost mean force-feeding themselves, but anyone who really wants to, can gain weight by simply eating more.