This is more than just a set of blueprints. This project walks you through the steps of planning, designing and creating a storage center that has the look of a custom-made unit with DIY pricing.
This modular system is completely customizable, and you can add or subtract components to create a wall of storage and seating that works in any room. The tutorial also explains how to measure, cut and install crown molding, so your storage unit looks like it was built with the original house.
Many more
built-in bookcase plans on FreeWW.com. This one is from woodmagazine.com.

This bookcase is built to fit underneath a window sill. You can use any hardwood for this project but the most common are oak or pine wood. Build a bookcase that works great for a kid’s room and while storing lot of books and what knots it also takes up little room and adds to the room’s décor. Just follow these instructions for this easy to build under the
window sill bookcase.
Here is a plan for a tall bookcase that is fairly simple to build. This bookcase will fill a space from floor to ceiling and has ten shelves that are adjustable.