Hope I can post this . .
www.guineapigcages.comwww.guinealynx.comI don't have a guinea pig. I wanted one for awhile until I pet-sat one. Although I adore them, not for me. I used those sites when researching and learned a ton. If I ever got a piggy it would be very well cared for I can say. I bought and used Cubes for the pig I watched, it lived normally in a pet store cage though. (small and evil, but that's my opinion) However I didn't use coroplast as I was just watching it. I used a shower curtain and it worked great, have seen it work well for perminant piggers too.
Anyway, to answer your question, the first site is extremely helpful..especially with cages. It provides a whole bunch of pictures, ratings/ critiques of the cages, and there is even a section in the gallery for "alternative cages" which is exactly what you're looking for. Yes, I agree the cubes are hard to find. On the first site (guinea pig cages) they have a link and you can order both cubes and coroplast from the site!! However prices may be higher, I am not sure. I found my cubes on a shelf it wasn't labled for and it was on sale..box was a little beat though xD They only sell them before school/college as that is what they are meant for I guess. However if you look closely at office supply stores, some have them stored at the very top shelves for some reason. I have no clue why they don't just sell them year round. Hope this helps . .word of advice, be carefull if you decide to join the guinea pig cages forum people on there CARE about animals and most jump at you if you mention something they don't believe is correct. (at least in most cases it is NOT correct) I am a member but I don't post too often, if not at all. All is good though, great information, and they are trying their best to get the information across but to some people it scares them or makes them mad I've heard. (there is even a thread about this, not necessarily guinea pig cages site they are talking about, didn't mention) The other site/link is mainly for research, if you haven't absorbed everything about guinea pigs, that's a great place to make sure you know everything there is to know. Good luck with your new piggy!!
Also sorry if I ever referred to you not ever having a guinea pig before, I just had that in my head. Even when you said you had one before.