What do you mean? You can build muscle with any percent body fat.
I’m guessing you mean when can one focus on eating a surplus (which might lead to a bit of fat gain) to build more muscle. In that case I personally do not like to allow someone to gain a lot of fat while adding muscle. So even if someone is not super lean he can train to build muscle. In fact,building muscle when you have a lot of fat can help you lose fat more easily in the future in great part because of improved insulin sensitivity.
Not to mention that most people do not measure body fat correctly. See, in the pictures on the front page of my website I’m 9% body fat… a lot of people think that this is 4-5% and many claim to be 6-7% while they are much more fat than me.
Since nobody measures precisely I cannot tell you a number.
Thanks Thib….At this time my weight is 174 pounds and the percentage of body fat increased from 9% to 15% -16% … Is it preferable that I first reduce my body fat or should I start building more muscle mass?