Yes, it's been done and this book tells you how:
I have a copy of that book, but I don't know where it is at the moment or I would look up the how to stuff on the concrete roller malt mill and pass it along. I think that they used steel pipe for the molds and the rollers were large, like 6 inch diameter. It's been awhile since I read about it, so I could be mistaken. How to make the mill so that it was easily and accurately adjustable might be the biggest challenge. I've never quite understood the desire to make one's own mill as the commercial versions are relatively inexpensive. OTOH, I do understand the DIY drive. I have a lot of that in me too, and there's absolutely nothing wrong with that. Keep posting back and let us know how this project progresses.