Lots of options out there, use the "search forum" function at the upper right of this forum, right above the "Sticky: welcome rugged stitching" thread, you'll find lots of info. Here's a few links for you.
Ripstop By The Roll is going to be the best place to buy materials. Bear Paw Wilderness Designs is also good for some of the supplies the Ripstop doesn't carry.
I just went thru this process and ordered everything for my own pyramid tipi although I have yet to find time to start building. I decided upon dyneema fabric which proved to be very difficult to come by. Rip Stop was definitely the best source of materials but I also ordered supplies from ZPacks and Bear paw.
Here are links to various suppliers I compounded mostly from fellas on Rokslide or other forum sites:
Another vote for Ripstop. I got pretty much all my supplies for my pyramid tent from them and they were great to deal with. Check out their factory seconds, as well. I knew the material I wanted and happened to see they had it for cheaper there and I didn’t mind the different green than I’d planned on. Saved me some money and I can’t figure out what was wrong with the material to make it considered blemished.
I haven't made it, but if you want a 'kit' to decide if you really want to make your own tipi - this one looks to be a good value and a good 'starter' project: patterns-vest-cart