Well How I personally am making them is...
I open up paint.. draw the picture all up.. obviously avoid using white cause thats the color thats going to be removed. once your done.. download a free copy of the program Gimp 2.. awesome program. that program has the magic wand tool.. hold shift and click on all the white areas and click delete. make sure you have created another layer... set as translucent and move it to the back.
p.s: I'm not good at tutorials.. but I hope this helps a little. I would like to see more people making maps.