If i own an apartment building do i pay taxes on the rent that I receive from tenants?
Yes, but I have heard of some landlords who take some cash and dont declare it . Be sure to declare all money that is given by government agencies such as FIA and Section 8. These agencies actually send you a w2 at the end of the year, so you definately need to declare that income. If you are not declaring some of the rent that may come in cash, be sure to remember if you get audited and you try to say that your unit was vacant the IRS can always look at the name the utilities were in at the time that you said the unit was vacant. Alot of your rent money can be off set buy writing off your interest payments, as well as taxes, insurance and depreciation. You can also write off mileage to and from your property along with any other expenses that you put into your property.
Eric Medemar
you pay taxes on income
income is revenue minus expenses
money you receive, including rent, is income
stuff you pay for are expenses.
sometimes stuff you don’t directly pay for are expenses, too - like depreciation.
I’m curious how you became owner of an apartment building without a basic understanding of income taxes? I’m not trying to belittle you, just to get a clear understanding of what you do and do not know about running your business.
i don’t own an apartment building yet 
You don’t have to pay taxes if you buy real estate with a Self directed Roth IRA. As you receive rents you put them back into the IRA account tax free. One of the secrets of the wealthy my friend.