photoshop program is really good for these kind of images, it let's you do nearly anything you want. There are also other computer programs like coral. This programs cost alot though! so if it's the one off image you are wanting to create I would advise you to go to a local library or perhaps a university library, these programs will be stored on them. hope that helps
Draw by hand and scan in or draw using graphic tablet. Then make all the edges thick black lines then, I suggest on a new layer, add colour in a Photoshop type program