How do you shade a tattoo with a homemade tattoo machine?

To be honest I wouldn't suggest doing any tattoos with a homemade tattoo machine. You can pick up a good cheap professional kit off the net, google it. And as for shading the piece, you may wish to go to your local tattoo shop and ask a few questions and/or watch them. But do not use a homemade machine you will never really get the look your striving to achieve.