These are often found in bathrooms above the toilet or living rooms and bedrooms next to the fireplace. We have one in the bedroom that we use as an office. The nook is a result of the fireplace in the living room downstairs.
Depending on the room and function of your nook, this may vary. I have these in my office, so I am adding them about 24″ above the printer and then about 16″ apart to accommodate large books and have enough space above them.
Use a stud finder to locate and mark the studs in the walls.
Measure and cut the 1×2 boards for the shelf supports. Each shelf has one long board for the back and two short boards for the sides.
The most common issue with homes is that the walls are never straight or flat. For example, my nook is 18″ in the back and almost 18.5″ in the front. This means that you cannot simply cut a rectangular piece of plywood for the shelf.