Rope usage is something like 25 metres per 0.5 metre of the 75mm pipe. If you get longer pipe - just multiple by the additional 0.5 blocks used. If you get wider rope (like 8mm) - this is great for the purpose and more importantly you need less metres.
A good idea that I need to try. My cat goes through store bought scratching pads very quickly and I need to put down my soldering iron for a change and make something like that :-)