Do you put Grids underneath the coroplast?

If you are planning on putting teh cage on a table or something, especially if the cage is bigger and overlaps slightly, then yes you need grids on the bottom. The same goes for if you have a raised cage with storage space underneath.
You would need the grids on the bottom otherwise they will simply fall off!

If you are placing the cage straight onto the floor then no, you don't need a grid floor.

Hope this makes sense.

If you have a table that is large enough or a plywood base to sit the cage on then you don't need grids under the coroplast.

Was just letting everyone know that my cage is finished. YAY!!! I did as Ly said above and put a plywood base on the bottom of the cage underneath the coroplast. It is going to be on a table my parents gave us. The greatest news of all of course is that I'm going to go get my to piggies Midnight and Ralphy from the rescue tomorrow and bring them home. I am very excited and nervous at the same time to meet and bring them home. Anyways, thanks for all the advice on the cage. Next I will probably end up needing plenty of advice on what to do when they get home.