Should I loose weight first or build muscle first?

If you are overweight or obese then you should absolutely not even begin with exercising. If you build muscle underneath all that fat then it will make you look uglier and bigger. If you do cardio at this time, it would be bad for your heart, which has to pump for the extra weight plus the exercise, this can lead  to heart issues later on. For the first 6months loose the excess weight for the first 6 months by purely dieting. That is how I lost my weight, restricting my diet. I did not take diet pills, although it would have been a faster process. I have currently reached a plateau between 135-140. My weight loss goal was to be at 120. So I still have a long way to go. I'm excited. Once I reach my goal weight of 120, I will start exercising to maintain my weight.