The bigger the better. Mine are about 30ft wide and around 400 ft long. I wish they were a little wider sometimes, but if they are too wide it can be a pain bringing in barn sour cattle by yourself at times. I would have built them bigger but was limited on the space I could use. If you go wider maybe make them funneled at the front to make it easier to get the cattle in.
JEEZ thats is not what I was hoping to hear, this is just where the calves will be at night and then they will be put back in the cooler, and they still get excersised everyday, so I dont think I need 30x400 :'(