Got my tents today!! Two of the five look like they've never seen the outdoors, they're seriously beautiful. Which made it easy to pick the two I'm not going to cut up.
Anyway, I started in on my one-person tent, and I thought I'd put on here what I did in case anybody is doing a similar project in the future.

I quickly discovered that there isn't a space in my apartment big enough to lay out the full tent flat, so the first thing I did was cut it in half (4' wide, leaving a little extra for seams and to fold up the side of the "tub" on the cut-off side) and cut off the top of the "pyramid" at 3.5'. Then I laid it out and figured out how much narrower I wanted it to get towards the feet. I sleep with one leg bent 90 degrees at hip and knee, which means I require a little bit more width at the hips than I honestly take up. So I laid down and measured, added a couple of inches so I'm not hitting the sides of the tent, and determined that I really ought to plan on needing 30 inches of width at the hips. So I chopped off the excess at that point. I don't require the extra space if I'm just hanging out reading a book or whatnot, so this is plenty of room This gives me a lopsided quadrilateral base for my tent.

Next, I evened up the smaller triangle at the "foot" end of the tent. It will finish at 2' tall, which is probably taller than really necessary, but that's how the angles came out. I left the original seam intact on the front corner and cut the other side to make it an equilateral triangle.

The harder one is the "head" end triangle. This is where the entrance to the tent is. I'm using the original zipper, which in the original tent was vertical. I used a little trigonometry and figured up that I needed the sides of the triangle to be about 3.5 feet long to give me the height I want. Notice that my first step was to cut off the top of the pyramid at 3.5'. This is where I got that number. So the next step was to cut the front corner seam and the zipper free of the rest of the netting on this triangle, and bring them together at the center point (creating a second equilateral triangle). I marked where they came together and cut off the extra netting (leaving a seam allowance as always. Then I sewed the zipper and the other seam back to this triangle with a "flat french seam" (I think this is the right term; it's a French seam that's then been sewn flat instead of just being ironed. This makes my tent tall enough at the "head" end that if I sit up very straight, I will hit my head on the ceiling.

Next, I cut a straight line from the top of the "head" triangle to the top of the "foot" triangle, along the netting that will make up the "front" of my tent.

That's as far as I've gotten at this moment, my next step is to cut pieces from the fly to form the rainproof portions of the tent.