Lissie has a plexi front that looks about 6 inches...I'm building a new plexi cage that I think will be 7 or 8 inches high all around so I don't need to worry about possible escape attempts
Mine has a 6 inch high and a 9 inch high plexiglass. The one I had the baby in is 9 inch high. Keep in mind that the height depends on how adventurous your pigs are and if they have reasons to want out of the cage. Some pigs are known to climb over walls (even with the 14 inch grids).