I used 6-7oz. top-grain cowhide stained to look nearly identical to elk hide. The pattern I used for both pairs is a modification of one I found posted here in a thread entitled "half chaps or leggings", posted on the forum entitled "patterns and templates". I modified this basic pattern to have a more symmetrical look all the way around, with no overlap/underlap at the heel. This affords a more finished look, and also allows a gap for spurs to protrude out from the heel of the leggings, without interference. The finished product looks great... almost like someone sawed off the bottom half of a pair of full-length, step-in shotgun chaps.
My template negates the need to sew on the top "knee flap", which flips up to offer additional protection for the knees while horseback riding. I also added an integral strap to the top of the template, which eliminates the need to sew on an extra strap and buckle for cinching the botas on below the knee. Instead, I sewed Velcro to the top (and strap) for fastening, which is the preferred method of attachment for most English style half chaps, and is a lot more comfortable than having a buckle grinding into the side of your knee.
I put my botas to the test, recently. I went horseback riding with my wife, and during the ride, we jumped a mountain creek that runs through a narrow gap between the mountain side and a drop-off. My horse shied away from the drop-off, hugged the mountain, and scraped my lower leg on a tree that was growing out. The botas protected as planned... the whole reason I became interested in making a pair in the first place, (full chaps are too hot to wear in the high desert mountains where we ride). Fortunately the tree didn't damage the botas other than to give them a little authentic "wear" in the form of a minor scuff.
Please feel free to comment, critique, or ask questions.