Is it easy to make your own UI/UX/skin on top of Ubuntu?

I have a few ideas that (I think) would make a killer experience on the N900 (and any larger tablets). I have these as .bmp images for you to peruse but I've only completed (e-painting) 2 segments out of the 4 I planned.

So if its easy/fairly easy my idea could be useful (purpose of this question)