Should I buy Crysis or Crysis Warhead?

Okay so me and my dad are building a super comp. It will cost me $1,300. I have $1000 so i have to work to pay it off. I want Crysis but I want the sandbox and mod tools and stuff. What I need to know is if Crysis: Warhead comes with the mod tools and sandbox. Or if i have to buy Crysis to get them. Also how much better is Warheads multiplayer compared to the reg game?