I used ash for mine as its lightweight- its often available on disused train tracks and the area I found had been copiiced so it didn't kill the base plant. Be really picky about straightness or they 'roll' inwards and make puckers
The liners were also called shadow cloths, preventing enemies being able to attack 'shadows' of the occupants at night when they were backlit but the main function is to form an exterior chimney for air draft. If you can get your hands on the
Laubins great book, it has various patterns and super info
I downscaled the patterns to make one for festivals out of a tip find and took the recycling theme through so used engine parts (valves for the pegs, push rods to stitch the front etc). It did well for a few years before I retired it
Heres a
facebook album of its make.
I had a 2 part liner with groundsheet, worked a beaut- I had it in the woods a few times over winter but the fabric was awful noisy and lost heat very quickly when the calor stove went out
One of the main problems I found was getting all that fabric under the machine to seam it... otherwise its good fun, make sure you post us a thread of your make so we can cheer you both along!!
PS My liner attached to a rope around the poles, if you put a llittle stick on the inside of the pole underneath it, the water tends to wick down that rather than drip. My main rain malfunction was the door facings made 2 drips but I used to pull back the groundsheet and it'd soak away anyhow
I'd avoid sectioning the poles because you'll affect the tipis strendgth- I erected and slept in mine in a field with 70mph wind and horizontal rain once and the bowing of the upwind braced back poles was frankly scary! They make the point in the Laubins book of avoiding conductors so avoid metals, they had lots of lightning deaths when they moved over to western supplied poles apparently.