Ive also looked into building some homemade feeders. I found on the web some ideas that use a peice of pvc (of you choice of size) with one end capped off and it strapped to a tree. The corn or feed will just pile up on its on and when the deer eat, they will cause more feed to pour out.

And of course you can always make a feeder with a plastic drum or bucket with a timer motor like on the manufactorer models.