roost size - spacing and dimensions

Hello Folks,
I hav the walls of the chicken coop done now, and want to design
roosts and laying boxes.

I have read much, perhaps too much!

So, now I am confused.

What should the dimensions of roosts be - figuring standard size
Chickens?

Could one use the 16" centers between studs in a wall as width
dimensions for neting boxes? this with a piece of 1/2 inch osb should
leave a 13" wide box - The question is what depth and height then?

Advice welcome.
Thanks,
Martin