Office buildings

[Grant Williams]

I am currently 16 years old and planning to pursue a career in commercial real estate. My goal is to buy office buildings and build a portfolio consisting of 1 million or more square feet, however the problem is figuring out how to start. I want to graduate college with a degree in business and start investing as soon as possible. I do not know how I can invest without any money. Also, I was trying to build an imaginary portfolio and see if I could cover my expenses and mortgage, did not know how much exactly the expenses were, however I was able to cover the mortgage with a substantial amount left over. I was wondering should I borrow a large amount to buy all of my buildings from the start since it can cover my mortgage and most likely the expenses or should I build my portfolio in stages(by the larger properties first and pay off the loan before borrowing to buy other decent sized properties)? 

Sorry my question was so lengthy, a response would GREATLY be appreciated. Thank you:)