Jon,
rolling a bait is a totally absorbing way of taking fish, it pre-dates todays static methods and on the day can and does often out fish a static bait. It teaches you about the swims you fish and indeed as it is primarily a roving technique, the fishery as a whole.
It is my first love when Barbel fishing, high water or low, I learned it on the Severn in swims as described earlier by Steve Williams back in the 1960/70s. I use a fixed paternoster set up by tying a dropper of 6lb line to my 8lb main line, then adding weight to the dropper. In low flows 1 or 2 swan shot rising to 1/2 ounce as current demands, I do the same as Steve, run the bait through a few times on different lines. Don't worry if it hangs up, leave it for a minute to give fish a chance to swing across the flow to investigate. If no one's interested lift the rod and let the bait move down till the lead hangs up again, and so on down the run. If you fish the line too tight to the weight it won't hang up, too much slack and it won't move, it's a trial and error thing.
Meatballs were made for this, if fact they are heavy enough on their own to cast and roll, especially in low clear conditions. As previously mentioned fishmeal paste, Cheese paste, Spam are all excellent and have the advantage that the hook can be buried in the bait to protect the point. I use mono, tried braid didn't like it, you don't need it, mono transmits every thing you need to know, hold the line between left thumb and forefinger and follow the bait with your body as it rolls down the swim. It's almost impossible to describe in text what constitues a bite apart from an obvious pull but interpreting whats going on at the business end is all part of the fun. Good luck with the method, it's like most active fishing techniques i.e trotting, practice makes perfect.