I don't know if you are serious, but I know that no one here will give you a serious answer. I'm going to assume that you live in the US. You want to be a cop. OK. That means you begin as patrol. Patrol, depending on location, makes between $35,000 and $50,000. It will take several years to be able to afford to buy property to lease since the federal government will take $5000 to $8000 of that right off the bat. It goes up even higher if you live in a state that has income tax.
Rental property is difficult. Everything has to be up to code and you will most likely have to make upgrades so people will want to live there. You have to price rent so that it covers more than the cost of your mortgage so you make a profit. In order to get a mortgage that low, you have to put more money down on the property.
ex. You buy a rental property for $250,000. It has two living spaces. One above ground and one in the basement. The basement needs $15,000 in upgrades to make it livable (you can negotiate this in the price but for the sake of the ex you don't). You have to take a loan out for $265,000. Let's say you put 10% down (standard practice). That means that you have to pay about $26,000 down to get the loan.
Impossible on your salary. It will take several years to accumulate that much wealth, assuming you can. Remember that life happens and you can get screwed by an injury or illness. Chances are good that you won't be able to do this and even if you could, you won't get "rich" in the process
*Source- Am an accountant/mutual fund manager