Advice on parts for an new PC build

I want to build a new PC. I have a 700- Watts PSU, an old graphics card (AMD HD 7870). The computer that I'm using right now has loads of RAM (8GB of Corsair Vengeance 2x4GB 1600Mhz) inside it that I can also use. Now, I need an advice so I can make it low on cost. What are the other parts that I need that can work with what I already have? Thanks in advance.
