Teri, I would never tell you that you aboslutely, positively could not make this a D-I-Y project, but I do not think that it would be safe or cost effective, based on what I have seen on the various home improvement TV shows. It takes special equipment to handle and cut the marble. Even polishing it is not something you do with plain old sandpaper. Diamond tipped saw blades are not exactly inexpensive either. I would be surprised if many stonemasons would trust your measurements so sourcing the marble in custom pieces could be a problem. To sum up, I think not.