I whipped this up last night. Probably didn't take more than an hour, it's really simple. I based it on some plans I found on the internet. Instead of putting in the strips to hold the plastic I just cut a groove in the sides. Much simpler. The window is dark because it's the only piece of plastic I had around. The plastic actually came from one of those little plastic file sorter bins that you stack on your desk. The groove made by the regular blade in my table saw was exactly the right width to take the plastic.
I put it way up on the tree (probably 8 feet or so) because that gets it at the right height so it's eye level from the deck. It's also about 10-12 feet away from the deck. I'm hoping when the squirrels find it they will be there all the time. That should make Seven really happy! The squirrels will be right there for him to stare at and bark at. The squirrels around here are pretty brave, so I'm hoping they'll figure out he can't get them when they are on it and will just ignore him and eat away. Which of course will drive him nuts.
I still need to get some food for it. At the moment it just has a handful of pecans that I picked up from one of my pecan trees.