Becca, building a bike from the frame up is really pretty fun. You'll learn a lot about the differences between cyclocross frames, mtb frames, and touring frames. Funny thing is, you will hear MANY opinions about what makes the best frame for commuting. All opinions have merit. You will be able to make your choices based on your knowledge. You will also end up with a bike that is truly yours. Good luck. Above all, have fun!

PS. I've been commuting/touring 22 years. This spring I get to start on my bike (built from frame up, piece by piece). I can't wait!