For my homemade Groot costume, I used pipe insulation tubs for the body and gym mat flooring that I carved with a hot knife for the chest pieces. I used over 140 full size glue sticks to attach the pipe insulation tubes. I soaked tissue paper in white glue and applied to the tubes for the bark however looking back I would recommend using a light fabric instead of tissue paper so that when you get into the suit and move around it doesn’t tear as easily.
I had homemade stilts with boots attached to them for the height as I was over 7′ tall in the costume and i am normally 5′ 5″. The head was made with 2 part foam and then sanded and dremmeled to get the shape and texture then covered with tissue paper soaked in white glue. I foamed in a snowboarding helmet with a strap so it would be easy to wear and would not fall off.
I am sure my finger will never get feeling back from hot glueing that many pieces on. It took me 2 months to make working on it evenings and weekends. It was a HUGE hit at parties and I was told numerous times that it was the best costume people had seen. I enjoyed all of the happiness that it brought to other people when I wore it. Everyone wanted their picture taken with GROOT!