Do you have experience wiring vehicles? If you've not done it a few times before I would suggest buying a kit.
Its hard to buy the parts at the price of the cheaper kits. So unless you have some real good reason for creating your own wiring harness, I think the smart move is to buy one.
That said I've wired several from scratch. I might do it again, but only if I'm convinced I need something a kit won't support. Right now I've no idea what that might be.
