My shelving is setup so the lowest shelf above the bench is 30cm, so it does not get in the way of the bench, the shelves above that are 40cm.
My bench is a standard twin-pedestal office desk, but I have adjustable shelving on the wall behind and to the left of it.
The left shelves are all 500mm and the first one is at the same height as the desk. The rear ones vary, and have an odd arrangement where the first, at bench height, is 300; the second at slightly above the top of a computer monitor is 400, the third is 200 and used for small books, while the top is 300 and used for large books and folders.
This allows fairly large instruments to my left, a monitor that's off the main desk surface, and the larger books well out of the way while the smaller ones are accessible. The desk, but for the bottom-level instruments and the monitor, is effectively 2m x 1m. It's more crowded thanm I'd like, partially due to my poor tidiness but it does allow a lot of flexibility without any custom building.
The desk has small devices such as a soldering station but the only instrument that intrudes on it is the fron half of a logic analyser : the back is on the rear shelf, so it only uses a corner of the deskspace.