You can find the details of the dimensions here:
http://www.firstinspires.org/sites/d...ifications.pdf
Personally, we thought 12 by 24 was a bit long so ours is 12 by 18 at its longest point. It doesn't have to be a rectangle. I created a
corn-shaped standard for ri3D and we have a more
traditional-shaped standard for the FRC team.
Other than that, we used the specified OD for the poles. If you have any more questions, please feel free to ask!