Ororeke,
Congratulations on your new addition!
I got my materials from Blokker. Not all stores sell them, although most do use the cubes to display material. The cubes I used for my first C&C cage actually weren't on sale, but were cubes that the store could spare. A few years later I managed to find a Blokker that was also selling them (in Wijnegem shopping center).
The coroplast came from a sign store. It's not known as coroplast in Belgium though, so try asking for "vikuprop" or "duoprop" instead.
I had laugh when I saw this thread. Phoebe will be turning 5 this year, and since my original post she's grown to be biggest & chubbiest guinea pig of the herd. I haven't referred to her as "little" in a really, really long time.