The six-feet tall part would definitely be a challenge. I'm thinking you'd need like a large cardboard tube (an empty tube that carpet comes on? or are there large thick cardboard mailing tubes? or is there such a thing as a giant dowel?) But then you have to put it into something that won't topple over from the height and weight. Well if it was wood, it could be nailed to a wood base that was buried in a very large flower pot with sandbox sand.
If you used multiple strands of yarn & used a giant crochet hook to create the stitch that fusbdgt gave a link for and then made a tube that way, gathered the top, just put fiberfill in the top part to maintain the roundness, pulled that over the more solid object, then do tube arms shaped with wire & fiberfill like starfishsea suggested..........
....maybe, just maybe it might work.
Definitely keep us updated.