Monique, I finished building my studio last year and documented what I had done on my blog--
www.caseychilds.blogspot.com (there's a link at the top left "The New Studio")
My studio was patterned after my mentor, William Whitaker. I patterned everything I could from his studio (within my limited budget) but, most importantly, the north facing windows. Because I work only from natural light this was essential to have. If you plan to work from natural light (daylight) I would recommend making use of the south windows. The goal with natural light is to have a diffused light, if you use the east window you'll have too much direct sunlight and would be impossible to work with, especially when working from life. You'll find on my blog a post dedicated to my choice of wall color which you might feel is a little dark but it's a beautiful color when working from natural light. I would recommend some neutral grayish color on the wall so you won't have light bouncing around and causing distractions when painting. Painting is hard enough as it is. The sink is a wonderful idea, I haven't regretted mine one bit. If you can, I would recommend a DEEP sink. It makes things a little easier when cleaning up and such. Oh, and I threw down laminate for my floor since I've got a concrete floor under it. I was worried about it at first, not being wood and all, but it's actually been good. I don't worry about spilling stuff and "ruining" it with my everyday studio activities because it's only laminate.
It's nice to have a floor where you can move things around on it easily, which is why I would recommend putting everything on wheels--easels, tables, etc.