I will say it again.
Check your pattern.
I was after a 12 oz 2.5 Apex quilt so I cut it very slim. Ended up at 12.8 oz, but its too narrow for the ground. It was intended to be a summer quilt for a hammock so it will work for that, but the next one will be wider.
I even blew it after building a test quilt a year or so ago. I still missed it as I was mostly driven by my weight goal which was a mistake.
Originally for my test quilt I made a year or so ago, I got some $1.50 per yard ripstop from walmart and some bonded batting from joanns on sale for $9 and built a test quilt. Just a straight taper, but now I think the shape below would work much better than a straight taper, but heavier.
The joanns quilt cost me about $18 to build.
A lot of work but recommended to work out the bugs and it will go to the grandkids.
I would suggest using anchored line locks and a snap, button and loop or something at the top of the zipper. Maybe at the bottom too. If you use velcro it does not matter, but I like the zipper.
This is my latest pattern that I think will work for me, but I am 6'-3"
It is based somewhat off a golite ultra 20 only the sides are straight for 30" then taper.
IMO 3'-6" is about minimal for the top and 3'-0" is about minimal for the foot area for a drawstring bottom. If you sleep on your back like in a coffin it can be narrower in the middle area.
I think the new pattern below will work better for me than a straight taper since I am a side sleeper. It should cover my knees and but better.
If you are unsure about the width like I was just start out with it wider and tack the last opening and try it out. Just put in the side loops later.
After I finished mine and realized it was too narrow, I thought what a dumb#$%^ I am since if you want to make it more narrow, all you have to do is rip the closing seam turn it inside out, Sew and trim off the excess and redo the loops.
Here are some pics of the last one I put together if you are interested.
Here is my last pattern. Have not built this one yet.
Here is roughly a factory Golite ultra 20 tall.
It has a footbox so its 5" shorter. I slept in the golite ultra 20 in a hammock at 14dF so I know that size will work pretty well for me in a hammock.