Calf Creep Feeder - Help?

I am wanting to offer additional nutrition for our calves this winter. I looked up a portable calf feeder but they want a large amount of money for these units and I never see it paying off based on our small herd. Ideally I would like to build one but I need some HELP!

I would love any information on a calf feeder you built or purchased. I am specifically looks for the width of the entrance. Not sure if they have individuals stalls but if they do those dimensions would be great also.

Thanks in advance for the information!!