I've made one myself, it's not yet complete and has taken ages, but I'll give you a quick run down.
It is made with a pair of OD Green overalls, on the front pressure points I've sewn green canvas. I cut the hood off an old field jacket and sewed it the the collar. From there I collected a massive amount of various items used in the construction. Old DPCU shirts and pants, greens, and hesian sacks. I spent ages cutting them into strips approx 4cm wide. The hesian I pulled into single strands. I then sewed all of them to the suit. That takes the most time and effort, and a willing helper. It is difficult because you think you've got the coverage just right but when you look at someone else wear it you spot gaps that don't work properly. It's just a matter of time and effort and collecting lots of old bits and pieces. Good luck.
By the way... we call them Yowie Suits