Nope, not me, but Kevin is. It was a bit difficult at first, having to follow directions from him, it's a good thing we get along so well. I think he thought he was supervising his guys at work (ha,ha!).
As far as the tubes - I believe they were from large rolls of carpeting, but I'll double check with hubby.
The carpeting - ugh!!! We had the same problem with it being so thick. Actually, what I tried to do for the corners was separate some of the padded part so it was a bit thinner - it was still very difficult to fold under. The first time we attempted it - we used a staple gun, but I didn't feel comfortable that would hold. Then, Kevin thought about screwing it in. That's what we ended up doing. However, be sure the screws aren't too long that they go through the other side of the plywood and carpet. We didn't have any real plans for the tree - just went to the local pet store and checked out different styles. I did a rough sketch and we guesstimated on sizes and did a few modifications.
We did put a shelf-type (carpeted also) piece of plywood in each of the openings on the bottom roll.
I wish I could be of more help. If my girls didn't love this thing so much - believe me, I wouldn't be planning on making another one anytime soon. I'm hoping the next one will be a bit easier - I'll keep you all posted.