A lawn roller was the first thing I made when I got my tractor. Mine is made out of 24" PVC Pipe used for sewer. It is 7' wide and filled with concrete. I made the ends out of 3/4" Plywood. My hitch is not as impressive as many of the others but has rolled my 3 acres 2-3 times a year for the last 4 years plus my neighbors use it and I have had no problems.
I made the plywood ends and drilled for the axle. I then removed one end and stood it on end to fill. For the axles I used 1 1/2" round stock with a 4" piece of 2" pipe slipped over it. Where they are attached to the hitch frame I put a grease fitting to service prior to use. I had to carry all the concrete up a ladder in buckets to pour in. I had 36 bags of sac concrete in it plus the weight of the pipe itself. I am guessing the pipe alone weighed in at about 400# and there is 3,000# of concrete for 3,400# total.
Chris