So I made my first cube today, following the directions in the 2nd post (The flickr album). Very good directions and the pictures are so helpful. It was not difficult at all (although I would add that you should clip the seam allowance on the circle, before you turn it right side out -- this will help with the bunching -- and then run the stitching around the outside of the circle to hold it nice and flat.)
The only problem was that there were no sizes mentioned. So I cut all my squares 300 mm x 300 mm. The cube is HUGE, and the rats have to JUMP or DIVE into the hole to get inside, and then it's quite a feat for them to get back out again! LOL.
Next one needs to be smaller, and I'll need to adjust the position of the hole to line up better with the shelving so they have easier access in and out.
But all in all, GREAT INSTRUCTIONS. Thank you!