I made one. You can either buy 5 meters of material (more if your say bigger then a size 14) or 2.5 mt of a wider material & cut that in half & then join it to make the length right.
Materials, I used a cotton jersey knit, it has some stretch to it but not too much. You want a little but not alot.
If you google "how to make a wrap carrier" you should get plenty of hits. There is one site thats good, just got to remember the name.....

eta- ok google that exact phrase I mentioned & the very first site that comes up is the site I was thinking of.