There are just so many different ways you can make nests and so many different things you can use. You might find it interesting to look through these. A lot of the photos have disappeared over time but there are still a lot there.
Opa’s Rollaway Nest Box
People come up with all kinds of rules for what is required in a nest box, but the chickens don’t bother reading those rules. There was a recent thread on here (with photos) where a chicken was laying on a shelf and went broody up there. That person put an old table cloth up there with padding underneath so the hen could at least make a nest. That breaks all the rules. There are still some things to consider.
A real common size mentioned for full sized hens is a minimum of 12” x 12”. I’ve used a cat litter bucket (not bin, bucket) that was 7-1/2” x 11-1/2” and open at the top. Full sized hens used it to lay eggs. I even had a hen go broody in it and hatch eggs. But there was a problem with that. The first chicks that hatched crawled up on Mama’s back while she was hatching the late-comers. When they fell off they missed the nest and went to the floor. They were not hurt, I just tossed them back in. That nest was so small she was sitting real close to the edge. That nest was fine for hens to lay in but not a good one for hatching chicks. I retired that nest after that. If you are planning on your hens hatching chicks you might want to assure the nest is big enough or shaped in a way she won’t be sitting right at the edge. Having it enclosed on all sides except where she enters and giving her room to get away from that entrance works well. If you are not going to be hatching any eggs in it, then this is not critical.
When a hen lays an egg she stands up. There are two different systems that wind up at the vent, the digestive system and her internal egg making factory. To keep the egg clean and stop it from coming into contact with the end products of that digestive system, a bit of the egg making part actually extends out of the vent to deposit the egg. It’s sort of like turning a rubber glove inside out as you are taking it off to keep your hands clean. To keep the part of her egg making system that sticks out clean she stands up enough to not let bedding touch it. I don’t have a magic height the top of the nest has to be if your nest has a top, but a lot of the bins I see at Walmart aren’t all that deep unless you get a really big one. You are probably looking more for a cube than a flat bin.
When they enter a nest, hens will often perch on the lip out front. Some of those bins aren’t all that heavy. When a hen perches on the edge it could flip. A common way around this is to build a frame the bin sits in so it can’t flip, yet you can lift the bin out if you want to empty it. The front of that frame can be that lip they perch on.
That hen that was laying on the shelf I mentioned ignored this part, but it’s fairly common when a hen goes into a nest to lay that she rearranges the bedding to make that nest just right. If you have a really low lip on that nest, she might scratch out all the bedding and any eggs already in there. I like a lip about 5” to 6” high so I don’t have this problem, but many people manage with lower lips. That’s a suggestion, not a rule.
Again that hen on the shelf ignored this part but many hens like to think their nest is kind of hidden from predators. This is not as important as some people think, but hens will sometimes lay in corners or under things that look safe. Even shadows on the coop floor can sometimes make a hen think it’s a hidden spot. I’ve seen plenty of hens lay in some wide open pretty bright spots, but normally it helps if the nest is not real bright.
One trick to get a hen to lay in your nest is to put a fake egg in there. I use golf balls but others use ceramic eggs, wooden eggs, or even those plastic Easter eggs. I’ve seen a hen that normally laid in the nest lay an egg on the coop floor next to a golf ball that got scratched out of the nest. She resumed laying in the nest when I put the golf ball back in and raised that lip a bit. But there is one member of this forum that said they had a pullet that would not lay in a nest until the fake egg was removed. There are no rules, a chicken will do what a chicken will do. The sure have no interest in doing what you want them to do.
I have had full-sized hens use an opening 8” wide and 6” high to enter a closed nest. I prefer the opening to be a bit higher but when you need to raise the lip you do what you need to do.
I don’t know if you will get anything helpful out of this or not. Try to make it convenient for you, the chickens can be pretty adaptable.