Will it be okay if i skip thighs and calf muscles exercises and concentrate only on upper body?
If you are looking to gain weight it is essential to work your lower body as well, even if just for metabolic balance. As the largest muscle groups are in the legs (glutes, quads are rather large as well) you will have a better hormonal response to weight training if you work these muscle groups as well. Working these muscle groups effectively primes the body for growth. Your Upper body will grow more quickly if you engage the large muscles in your legs, as well as having the benefit of overall making you stronger. Squats and Deadlifts are more or less essential to any workout in my honest opinion.
