I have always run a one wheel Velke brand sulky on my walkbehind. It speeds things up substantially and eliminates the fatigue. I wouldn't go without one.
Personally, rather than going through the trouble to build a decent sulky, I would just buy one. Most off brand sulkys (Havener, etc.) aren't bad. The only reason I have a Velke is because it came with the mower.
Ford Trucks-Gravely Mowers-Stihl Handhelds