I’ve done up a couple of rope halters. End results? They work fine. But I will BUY THEM forever more. Just not worth the hassle!
If you’re looking for a sidepull just buy one. They come cheap.
PS: The halter you linked isn’t a sidepull, anyway. It’s more of a bitless bridle with action on the rings = tightening under the jaw. I’d rather have a straight sidepull, which you could accomplish pretty easily by just knotting rings into your side nose knots, were you so inclined. No complicated rope arrangement required.
Or just buckle your reins onto your current halter. This ain’t rocket science.
(BTW leaving a free end on your lead line like in [url=http://4.bp.blogspot.com/-uyRaghVfHtg/UmLHhiSePuI/AAAAAAAAScg/otLri_V7FCQ/s1600/20131018_170524.jpg]this pictureis a bad idea if you ever hand graze your horses. You’re just inviting your horse to step on it and pin their head to the ground. Learned that one the hard way, on a thankfully very kind horse…)