Next week I shall mostly be building my Prusa i2 3d printer, thanks to Julian.
Very tempted, what software are you planning to use?
Drawing wise I'm getting into sketch up, all other software will be as recommended on the build site.
As a bit of practise, you'll need to mount the Arduino on something. I fabricated (read ... cobbled together) something but if you want to print a more permanent mounting you could start with the attached file. I drew this to space an Arduion board off the table so you can play with it, but it could easily be adapted for fixing to the printer frame. I've mounted my electronics to the front right.
As the file opens, the right hand end will be the end with the power and USB connections.