In all honesty, yoga is not the best approach if your goal is to build muscle. If you're a total beginner strength-wise and really want to do yoga, I would recommend ashtanga, but if you have a baseline in strength and/or just want to build muscle, your time is better spent doing some form of resistance training. Yoga can be a great workout for sure (and possibly even more importantly a form of meditation in motion), but using only bodyweight resistance on the floor makes it difficult to sufficiently strengthen the posterior chain muscles of the body (responsible for pulling and hip extending motions). Ashtanga is quite dynamic, but many other yoga forms focus on static holds only, which are not the best way to build muscle. Also once you achieve a certain level of strength, you have to get really creative in order to strengthen the legs using only bodyweight. In my opinion yoga doesn't have that kind of variety for the lower body.
Of course you could do yoga and supplement it with some additional and well planned strength training, doing upper body pulling movements and hip thrusts and hip extensions for the lower body. In my opinion those are very much lacking in all forms of yoga. This would be a good, nicely balanced approach that in time will build a strong, toned and flexy body :)