What tools will i need?

Uh, that depends. You can go with just a drill and sand paper if you want. You can also fancy yourself out with a Dremel or some other power tools. Anything that can cut through the metal safely without harming you will work - it's up to you on the quality and how it looks like - you might want to make the fan hole slightly larger so you can cover it up or have a filter or something on the outside because you'll probably make some defects on your first try.

You'll also probably want other things to mark the area you are going to cut (pencil and/or duct tape?). There are plenty of case mod guides out there though I'm sure that can give you far better tips. The main issue is preparation beforehand and knowing where you'll cut.

dont forget the B.F.H.

LOL that ought to do it