I tried out your idea with my jumbo lego blocks. My guinea pig seemed to love it

! I connected them up to make some steps and at the end of the steps is a tall tower. On the tower I put a (already lego made) small T.V. thingy. On one of the side there is a square hole. I stuffed it with hay.
It didn't take long for my guiena pig so spot the hay and climb up the steps and streach for the food. Once he finnishes eating he runs away and waits for me to re stuff the T.V. with hay again, then scurries to the top. It's so cute

.
The good thing is that it's strong (coz it's made out of good plastic), washable, extreamly fun to play with and redesignable (so far I have only designed a tunnel/bridge and steps). I forgot to mension that it's colorful and really does brighten up a dull cage!
That's all.
~Octoberborn