Gain extra accommodations for overnight guests with a window seat sized for a standard twin mattress (39 by 75 inches). Popular additions to bedrooms, the oversized seats can also offer an inviting spot for a catnap in a home office or a den. A lowered or arched ceiling (shown above, covered with wood slats) adds to the snug effect. Install built-in bookcases and lighting to mimic the usual nightstand elements, or make the window-seat platform area longer than the mattress itself to give you extra surface area for placing books and other objects. If cabinets or drawers are included in the window-seat base, include a toekick so that it's easier to stand close to the bed when changing linens.