I agree with Garrett.
Building muscle and losing weight is fine, the bigger the muscles the more energy(kcal)they burn = weight loss!! lifting weight weight alone will help you lose weight!!
Running will help you lose weight but it will also help you lose muscle mass(not too much!) Your muscle mass changes to suit the activities you do. Which is a good thing because i can look smaller than some of the heavy gym users but still be stronger = KO them!!