This is not my mod, it was created by Bluntaxe. I've just updated it for SE.
File credits
All credit to Bluntaxe, original creator of this mod.
Donation Points system
This mod is opted-in to receive Donation Points
Note: This is not my mod. The original author was Bluntaxe, who I've tried to reach out to - but who does not appear to be active anymore. However, from their other mod pages, they don't seem like they would object to this as long as I give them full credit. The original mod can be found here. I have made two small adjustments - my version includes a fix to stop the books from falling off the shelves, and has adjusted the bookcases very slightly based on the Unofficial Skyrim Special Edition Patch.
Compatibility: Depending on the house, this mod either adds a small room, or it adjusts an area within the house to add the bookshelves. It's likely this mod won't work with mods that completely overhaul houses, but mods that make small changes still seem compatable. Best way to check is to test it yourself.
This mod is NOT COMPATIBLE with mods that edit books, including mods that change book covers.
There are books missing from this mod - I believe it does not include the Dragonborn books for a start.
If anyone really would love to see a mod that does include all the books, or is compatible with mods that edit book covers, or is compatible with x or y, I invite, encourage, and would love for them to create one. If I had the ability, I would do it myself - but I do not. I would be happy to assist with such a project though.