Brahma and orpington. And a giant olive egger mutant hen.
The olive egger has tried a bit honestly not sure they will actually start lating until spring. They were hatched in July. I haut got them two weeks ago.
Mostly thinking in advance .... The roost is filled with straw so if they want to nest outside box it isn't terrible
I build nestboxes 16" cubed, that is plenty large for Bielefelders, so I think Orps and any others will do fine also. I often see 3 Rhodebar hens at once in one of those, seems egg laying is a social event.
I only raise Plymouth Rocks anymore and I've always used a 12x12 nest. Sure they are not as huge as Brahma but a good sized bird. I'd wait and see how they take to it, two Rocks in 12x12 means a Brahma will fit easily. As for Cochin, don't get confused by all that fluff. It compresses easily to the much smaller bird size under it.
All I'm saying is if your start with large birds and need to build nest then sure, make the 4x14 or any configuration you want. But with nests in place why fix it if it ain't broke?
I’ve seen some full sized fowl hens lay in some pretty small places, but my personal preference is for nests to be a bit larger. It just seems with everything with chickens larger is less stressful for me than smaller, I just have fewer problems to deal with. That could be coop or run space, roost length, nest sizes, brooder space, just about everything.
I propose an experiment. Build one larger nest, 16x16, 12x18, whatever size fits and makes you happy. Then just add it without taking any other nest away if you can, especially do not take away one the others are using. If the other hens are using the current nests don’t change it around and mess that up. Then just see which nests they prefer, the smaller ones plus your larger one. That should take all stress off of you and let you find something else to worry about.
How might a smaller nest stress me? I let a hen brood in a 7-1/2” x 11-1/2” nest, a nest made from a cat litter bucket. That was a barnyard mix hen with Sussex, Delaware, Australorp, and maybe Orpington so a full sized fowl. I had the bucket and needed an extra nest so I used what was on hand. So there is an example of full sized fowl using a smaller nest. The stress came from the first baby chicks that hatched. They often like to crawl up on Mama’s back while she is hatching the later chicks. Of course they fall off. In that small nest instead of falling back in the nest they fell all the way to the floor. Three different times I had to pick a chick up off the floor and put it back in the nest with Mama. I retired that nest as soon as the broody hen finished with it and built a 16x16.