I have made many bags. See my video from last year I made
(1 gallon grow bags_. https://www.youtube.com/watch?v=8iBkfHxfhpI
(Video 2) 5 gallon and 1/2 gallon bagshttps://www.youtube.com/watch?v=RhwcSVaUO_Q
This link can help you chose what size bag to make. The more roots the bigger bag it needs.
Link to the amount of root a plant hashttp://itsgreenday.blogspot.com/search/label/Root%20depth