Pop Art Poster

I want an illustration of my two sons done in a pop art (Lichtenstein) style. I have a very clear view in my mind of exactly what it will look like. I would like to articulate this and get some outline images/sketches. Following some detail clarification I would then like the output finalised as a vector image so I can get it printed in a large format. Normally I am very flexible and allow some creativity however you should allow for a couple of changes to be made for the final output.