I am currently using Kreitler Challenger rollers with the fan unit. They are amazingly smooth. They are aluminum drums with PVC end caps. They are more expensive than other companies but if you do a search around you will find that just about everyone recommends the Kreitlers far and above anything else. They are guaranteed for life so if anything does go wrong then you do not have to worry and from what I hear nothing ever goes wrong with these rollers.
Good luck.
Mike