The differences between garden windows and bay windows are size, shape, and cost. Garden windows are about half the size of bay windows, and thus cheaper — although still more expensive than other window styles due to the need for additional framing and support. The sides of a garden window (which are venting casement windows) meet at 90 degree angles (rather than 45 degree angles) for a boxier shape than bay windows. A sloped pane forms a roof over the box to create a mini-greenhouse.