You have 72” across there and you want 10 nests. Divide 72 by 5 and you get 14.4”. So make two rows of five, one on top of the other. Make four of them 14” wide with the fifth one on that row making up the difference.
I’d make them a minimum of 12” deep and personally like them a bit bigger for a couple of reasons. It’s not that unusual to see two or even three hens on the nest at the same time. You can see some cute photos of a chicken laying squarely on top of another hen in a smaller nest, but I like the nests big enough so the hens can lay in the nest instead of on one another. Also, if you let a broody hen hatch in the nest, if your nest is small you could have chicks fall out. The earlier ones to hatch often crawl on top of Mama. In a tiny nest, they may completely miss the nest when they fall off. In a larger nest Mama is not as close to the edge so they are a lot less likely to fall out.
If you have a 4 foot wide sheet of plywood for the bottom and top of the nests, you will need three pieces of wood for the tops and bottoms of the nests, assuming you put a top on the top row. If you cut that sheet of plywood into four pieces, 12” leaves you no waste. If you cut it into 16” strips, you also have no waste. Both 12” and 16” will work for depth.
I like a fairly high lip on the nest, 4” to 5”. Hens like to scratch around when they are preparing to lay to get the nest just right. If you have a low lip, they can scratch out bedding or even eggs. I have had hens use a 6” tall opening to get into a nest, but 8” is probably better for full-sized hens. So I’d recommend a minimum of 12” height for a nest. Depending on how you frame it (if you have a support with thickness running across the top) you may need to make them a bit taller.
You can put the nests any height you want. People care about that more than the chickens. Some people put the nests right on the coop floor. Chickens like to scratch a lot, so depending on how things are laid out they might scratch trash from the floor into the nests.
Chickens can jump/fly pretty well. They should have no trouble getting into a nest a couple of feet or even more off the floor. Putting a pole or shelf in front of your top row can make it easier for them to use those nests though. It’s probably a good idea.
The way I determine height of things is to look at the height of the floor when covered with bedding. Then I position the nests. Then I make the roosts noticeably higher than the nests. The chickens like to roost on the highest place available. If your roosts are not noticeably higher than the nests, they will likely roost in your nests.
Hens go broody when you don’t want them to… and won’t go broody when you do. 
