When is it a good time to start building muscle?

My question basically is at what weight just i start to really push myself to build muscle? I am 235 and im trying to get down to 200 and then i was going to start weight trainning heavy and adding more reps to my weight trainning. Right now, im planning on just doing cardio and abs to lose my body fat. My question is, what weight should i get down to and should i even worry about weight trainning right now or should i just do a lot of cardio and ab workouts to lose this body fat and weight?? Thank you!