The simplicity of the Sling style baby carrier makes it and the wrap the most popular DIY 'models' for people to tackle themselves.
2 to 2 1/2 yards of Breathable Woven Material that doesn't have right/wrong sides since both will be visible when wearing.
(2) 3-inch rings (plastic or metal)
There is a product called 'sling rings' for this purpose that you can buy, as well. Metal ones can be a bit heavier and some would rather have a more lightweight option with PVC or durable plastic.