At age 16, how can I get my start to build up to be in the indy car series?

Like Ray said you need lots of money or a sponsor with lots of money. I hate to say it, but at 16 you are kinda a little behind the 8 ball already. Most Indy series drivers started in karts when they were 8 or 9 years old. Start racing karts as soon and as often as you can now. If you want to stay in open-wheel racing, I would then try to get a ride in USAC. By driving sprints, midgets, and silver crown cars you will gain valuable experience you can use later in your career. Talk to anyone and everyone you can about racing. At the tracks talk to drivers, owners, and sponsers. Get to know as many people as you can. The next logical step is to try and get a ride in the Indy Pro Series. This is a support series for the IndyCar series and often run the same tracks. If you are successful at this level it will only be a matter of time before you will get noticed by a IndyCar owner willing to give you a chance to drive their car. Good Luck!