The plans at the link are for a 3 foot floating shelf but adjustments can be made for a different length. This is a project you can complete in a day.
This floating corner shelf could work beside a bed or perhaps by the front door. Here is how to build and install it.
This traditional-style wall shelf could go just about anywhere and serve as a mantle or shelf. Here is how to build it.
Follow along as I build a shelf from stock lumber and crown molding. I actually bought some new material for this shelf. I needed a 2×6 and a 1×6.