Hi, hopefully this would help. When I did this costume back in 2007 I had this dilemma.
Eventually, I found a pants pattern matched, and then I sewed each separate of color together (eventually sewing the white strips on top of those), but still following the pattern. Then I hand sewed on two-inch white "stitches" all across the pants where each color came together.
so, in your case I would approach this depending on how you feel more comfortable. I felt a little awkward at first too. A little the same way, because it is quite a lot to handle. But ultimately I found that making the pants from scratch was the best choice, the only way to get them just the way I wanted. :P Hope this was helpful.