C&C Alternatives How high should the walls of a custom cage be

Theoretically I'd like to take the front off like I do when cleaning the cage (see pic) and have maybe 4" of acrylic along 8/10 feet then two normal (not Midwest) grids in the corners.

I think it depends on the pig. I've known of a couple that routinely climbed out of cages with 14" grid walls, and I've know some that made no attempt to get out of six inch walls. My own philosophy is that I'd rather be safe than sorry, so the walls of my cage are 16 inches.

I wouldn't do less than 6". Most pigs wouldn't intentionally climb over the cage wall, but I feel like 4" is so low it's practically inviting them to fall out.

I have a custom acrylic cage, and the walls are about 10" high. Since it is acrylic, they can't climb it and even when they are standing up, begging for food, they can't reach the top edge. However, they also don't seem to have much interest in leaving, so I can't speak for the Houdini pigs of the world. Is there a reason you don't want the plexiglass to be very high?

@ginipigsinspace the cage is on top of 3' bookshelves, and is 3' deep, so unless I take off the front its kind of hard to reach the back when cleaning. That's all.

and no Houdini pigs for me, but I have had Houdini fish. I kept show bettas for a while. One went missing for 3 days (was the only fish in the tank) then re-appeared once I gave up on finding the body. I had re-arranged the tank and everything. (Sigfreid and he had a snail named Roy)
another I ordered from a breeder, when I got him he had somehow lost his head in transit. (He was in a bag of water, in a bag, in a box of peanuts. The head was in the bag with him. Completely detached yet intact. He was Houdini)
And another was an ace at slipping the tank divider, going underneath the substrate, just getting into weird places. plus he had irids over black, so when you looked at him he was black, but in pictures he was sky blue. (He was arcnologia, reference to a wizard from the show fairy tail)
and Mesmer (after French magicians/hypnotists Messmer and Mezmer) lived for more than 2 years with "black gills" (blood poisoning) came to me white, eventually turned lilac, then dark blue, then dark purple.

My Coloplast base is 4 inches. I cut a hole in a grid and attach a ramp for floor time or extra running room. My piggies get over it without any effort so I definitely would go higher than that.

Since 3ft off the floor will be quite a fall if they accidentally go over the walls, I'd go with something taller. When people say they have 4 inch wall, it just means the coroplast. They still have the grids to prevent the pigs from falling off. (Grids are 14 inches tall)

When I had plexiglass cage, my walls were 10 inches on the top cage, and 6 inches on the lower cage.

If your pigs are seniors, you don't have to worry about them jumping too high.

If you have active pigs, definitely go with taller walls.