The size range is newborn to size 4. Which is about the normal range for body suits. It's fairly easy to sew and can be completed in under an hour. I recommend a serger, but you can easily use a regular sewing machine.
Buy the sleeveless bodysuit here.
The size I made was 0-3 months. The fabric I used was a slinky knit purchased at Joann, as well as Lycra. It's better to use a stretchy fabric that has a good recovery. The fit is great on Ava. She also looks so adorable.
If you like to sew, you should check out LittleKiwis Closet!