It's very rare for pigs to climb or jump out of C&C cages although it has happened. I had a baby boar once that climbed up the corner and out the cage or he'd climb up to the second level and do a mad dash and almost literally fly out the cage. After that, his second story was taken down and then his main level got a lid.
Grids are approximately 14" square. For young pigs, the cage will need baby proofed. Either higher coroplast walls or cardboard behind the existing walls to provide a higher barrier. Or even double grid the cage with lower coroplast walls. Safety must be the first priority when building a cage. Upper levels need to have grid walls so pigs don't jump or fall off. Ramps must be stable.
You may want to read the "about cages" forum and the "cage safety" forums before building your new cage.
Also if you have just the one guinea pig, consider adopting him/her a buddy because they do much better in pairs as they are social creatures.
