sounds like fun! Get photos if you can, where is it?
I don't suppose that was very helpful, sorry.... 

what size waiste well lets see...45 inches..Im a big boy

Im looking for a pattern if you have one

...how are leggings a primitive weapon?

You don't need leather for leggings. In fact if this is in winter, you don't want them. they will freeze and be cold.Trust me. I know.
  I would use a heavy wool. What the mountain men used to use were Hudson's bay blankets, or their equal. Making them is really no problem.
   Measure up to your inseam. This will be the "tube" of your leggings. From there, you need to make various  loops that will allow the leggings to hang from a belt. I usually also wear sashes at the knees, for further security of the leggings.
  If you want the fringes, just add one inch to where the seam will be. ( The seam will be on the outside of the leggings) Then sew up , leaving the excess. Cut them into fringes. I would also recommend that you blanket stitch any cut area of the leggings, to keep the wool from unraveling.
   When I klondike camp with my Boy Scou Troop, ( yes we tent camp in the winter) I wear my leggings, buckskins, and capote, and badger hat. let me tell you, I am warm!

Same basic procedure for the leather as with the wool blankets. If you are going " Proper", as in no pants under the leggings, you will need a breechclout, for obvious reasons.
   That is the way to keep the coolest while wearing them , but it's up to you.

I've seen some people use heavy cotton for leggings and breechclout too. Not really sure if that is exactly period, but they do look comfy.