This Instructable will show you how to build a corner shelf for little money and it takes little time.
Step 1: What you will need
drill, level, stud finder, drill bits, screws ( not pictured: square)
wood: 1x8 board and 1x3 board( I ripped a 1x6)
cut the 1x8 so it will fit in the corner( 45 degree angle)