I arrive in Rome on a Saturday, i need to change money to pay an an apartment rental as soon as i get there. I also need to change money for airport pick-up. where should i go, any suggestions?

Best way is to use your ATM card there. Make sure your bank knows you are traveling and that you will be using your ATM card there. Also if necessary ask them to increase your daily/weekly withdrawal limits.
I am sure there are ATM machines at the airport there, but if you want to be sure take along around EUR100 from any bank here just to have something in your pocket upon your arrival.

I completely agree with HenryH's reply. It is the best option.

Here is a link to FAQ forum which has a topic that has lots of info, including a topic about ways to have a large amount of cash available for arrival day payments.

There is an ATM machine at the international arrival terminal of Leonardo da Vinci Airport,
so you should be able to get euros immediately after clearning passport and customs control.