Construction is simple on this tree, which was a blessing after some that I've put together.  The size is perfect for my 9 lb cat - she isn't squished but she feels cozy inside.  There is just enough space between the weaving on the sphere that she can peer out from inside, which she loves to do.  She also really enjoys sitting on top of the sphere, despite the large hole.  My only note is that if your cat is somewhat graceless, you may need to weight the bottom.  When she leaps off, the entire tree shakes sometimes.  

Pros: Best looking cat tree I've had, easy to put together, fits in a corner
Cons: A little unstable