building decent .com domains

I thought many times of start building decent .com domains when having enough capital in the future, but I always struggled with a math in my mind, which kill off the idea, thought sharing this math, and let's see what are experienced dominers opinion? let see, I want to build a portfolio of...

I thought many times of start building decent .com domains when having enough capital in the future, but I always struggled with a math in my mind, which kill off the idea, thought sharing this math, and let's see what are experienced dominers opinion? let see, I want to build a portfolio of...