Now there's nothing like doing it yourself, you'll get a lot of fun and experience in that stuff. I've read, however, that the SlikStik control panels are very, very reasonably priced because they are getting great bulk discounts on every piece of equipment that they provide, so while they won't be passing all the savings to the consumer, they can competively price their product.
I've also read that their control panel is very well-assembled and lots of care go into building it so that the inside is as neat and well thought-out as the outside.
The only advantage I see of building your own control panel would be that you can create a more unique setup tailored to what you'll be playing. If you think the Classic setup is pretty much perfect (which I do), then I would go with that.
BTW, what kind of monitor do you got? One of those Wells-Gardners?