I am getting a cage that conveniently has a cage cover made for it, which also covers every side, including the front. During the day, I can roll it up all the way on all sides, but during the night could I pull it down all the way to cover all the sides, but keep it unzipped for air? Or is that cruel, blocking of all sides, or should I cover all but the front or top? I am mainly just afraid that they will fling poop/pee on the wall, or like pool when they jump and it gets outside. I am living with relatives that aren’t the biggest fans of me getting them soon, but don’t mind much but I think this is their and my main issue with them.

I would leave the back one down so you keep stuff of the wall. I would keep a vacuum cleaner handy for anything the lands just outside the cage. BUT night time is time for them to run around, play around, LOOK around. I would NOT put up a wall so they have nothing to see. Ours will see us and jump to the front, looking for a treat, or a ride on our shoulder, or a jump in our shirt. They check out the dogs and kids. To put them in the total darkness? during their awake time seems very wrong to me. they have good nighttime eye sight, but with a full cage cover will they even be able to see in almost total darkness?

You should probably leave at least the front uncovered, so they can look around like BYK_Chainsaw said. You could also get some sort of floor covering for around the cage to protect the floor from anything that might be flung out. Is the cage going to be in a corner, you could just leave the cover down on the sides by the walls if so.

I made cage covers that cover the backs, sides, and top. I have the front open. Better circulation. There are to cages side by side so I have the one side open to be open to the other cage.