Just for the record, Bob V. never answers on this site. It's kind of like how he made Norm do all the work on the show!
Anyway, As Moderator Steve mentioned about your earlier post, you may have to wing it as far as plans go. The 22.5 degree angles will work.
You might be able to find plans at Home Depot or Lowes or some other lumber yard. I might look in the big orange book of projects they have at Home Depot.
But, I would probably lay it out on a piece of graf paper.
You know the tree is three foot around and you know that you should leave about one foot between the tree and the bench, so you are going to have a six sided bench with a five foot diameter in the middle. Using the 22.5 degree cut angles, you should be able to draw it out for the first row and rest is easy!
I would decide what you want to make the bench out of and that will determine how many pieces of wood you will need to build the width you like.
Good luck, Jason
ps. You will still receive post (or not) as the week goes on. You do not need to repost your question after every reply.