Change your fill to a pale yellow to white gradient by opening the Color Mixer tool panel on the right-hand side and selecting Linear. It will default to a black-to-white gradient; you can adjust the way your gradient blends by moving the sliders depicted, and change the colors by clicking on the markers for them and then adjusting the colors using the picker. Once youve set your gradient, draw a small rectangle anywhere on Layer 2.
For this instance well make all the windows the same size so, rather than drawing in each individual window, were going to make the window rectangle into a symbol that we can then drag and drop over the canvas as we please. Use the arrow tool to select the first window drawn, and then go to Insert -> Convert to Symbol (shortcut F8). Ive named my symbol Window to find it easily in the Library, and set its type to Graphic.