I built a roller this summer. I had a patio concrete pour from U-Haul carts and knew I'd have leftovers. Prior to the pour I bought a Sono tube, made 3/4in plywood ends and used a water pipe shaft. I stood it on end on concrete blocks so the axle would protrude from the down end. You could also dig a hole for the shaft. I filled the open end shoveling from the FEL then placed the top ply end to hold the axle in the center. It's still curing

awaiting a frame.
Sono tubes (cardboard concrete column forms) are readily available at builders supply stores cut to any length and even box stores have some, but normally they have a limited diameter selection. Many diameters are available. I paid $12 for a 6ft x 24"dia piece. At 150#/cuft for concrete you can easily make the size and weight you want.