Well basically a traditional antivirus engine does nothing more than comparing file signatures against signatures of known viruses. (In real life it's more complex than that, but this is the basic idea.)
So in order to create an anti virus program you will need signatures of the viruses it should be able to detect.
But maybe you should get the basics down first. Like what programing language are you going to use to write the program? What operating system should it run under? What viruses should it detect and so on... Also what programming experience do you have? Because a project like this is not for beginners.
