I have made about 25 pairs from this pattern. I needed to modify it a bit to make it work - both for smaller and for larger feet than the pattern is made for. Also, the cuts going to across the mid portion of the foot - before it goes up to the ankle are much too low; they need to be cut about an inch higher than the pattern otherwise every bit of grass, stone, and dirt will find their way underneath your foot.
I made them out of moosehide, butterysoft and supple, though lightweight cowhide has worked well too. Sew the extra sole on the outside of the shoe with waxed linen or artificial sinew (and stay off the concrete). The basis of the pattern is easy to put together. I will look at my notes later and see how the angles and measurements were used to create the other sizes and modifications.
For what it's worth, the ghillies were developed to deal with the low boglike areas where a traditional buckled shoe would have been sucked off the foot at the best, or simply would have held a bunch of water against the foot promoting foot problems at worst. The cuts along the sides allow the water to squish out of them and drain away quickly, while still protecting the foot. When worn, the ghillies weren't laced up the thigh - they were laced around the ankle several times. Lacing strapped tight enough around the thigh to keep the ghillies on in swampy ground WILL cut off the circulation to the lower leg. Most likely the laces will fall around your ankles anyway. The long laces were to wrap 'round the ankle several times to spread the load of the pulling of the shoe in sticky situations.
Most people of means would have used buckled shoes in this time period, the less well off would have used hand made ghillies as described above.
I re-enact this time period, and have worn the straight lasted buckle shoes, and the ghillies for days on end. I have gone hunting with both as well. The ghillies are absolutely silent in the woods, and you can slip through streams, muck, and creeks without having to take your shoes off to empty them. They are comfortable as only a moccasin can be, and conform to your foot like a second skin.
Mark