Here's an easy way to turn a bookcase into a bed. No tools required. That's right: no drill, no hammer, no nails -- just paint.
What you'll need:
A sturdy bookcase. Ideally, this should be at least one foot longer (taller) than your mattress, so you can have a built-in bedside table. You can repurpose a bookcase you already own, or find a cheap one on Craigslist. Last time I checked, there were dozens. Or, if you're feeling really crafty, you can make one yourself. There are lots of Instructables that can show you how to make a bookcase cheaply and easily.
A can of paint. Whatever color suits your fancy.
One piece of plywood that fits over the bookcase, cut lengthwise into two planks.