Interesting... I've yearned this jutsu for a long time.
Yamato remembers. He remembers so vividly it's almost like he's there again. Focusing back to reality, he claps his palms together, and creates a huge amount of Mokuton chakra. He then channels this chakra into the ground. Once done, he emerges a large quantity of wood, in no particular fixed shape. He then molds this wood, and by using shape manipulation, gives it the ribs, spine, arms and a skull with a hole for eyes. Yamato then creates a large amount of tender, flexible tendrils/thin flexible branches. These tendrils wrap and coil around the humanoid Yamato has made, strengthening it. Finally, Yamato creates more wood. He creates a thick, huge circular shield which the giant humanoids arms hold, for defense that is. And for the other arm, Yamato creates a massive spear which it holds. By supplying constant chakra to it, Yamato makes his own homemade Susano'o levitate, so that if follows where he moves.
All hail the wood version of Susano'o.