I'm even planning on my living room having built in storage under all the windows.
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There're called Window Seats, and are in most of the more expensive decorating mags nowadays. They are also rather old fashioned, which is good because the older houses had very little storage. Usually they have the seats which have doors under them, or else the cushions come up and you can pull up lids to the storage underneath. I would suggest the doors or sliding doors myself, since I have a Persian that sheds all over the house and pulling the cushions up all the time delights the cats!. The sides of the windows are generally book cases, but even then they can have drawers built into them, later if you can't afford them right now.
Shelves to the roof on one side in closets. Closets around the outside of the walls for added insulation, built flat so you could hang over them a giant quilt for checking last minute details.
The same with a big flannel area.
Makes me want to have something like that to build...not that it'll ever happen but I love to dream.
AND LIGHTS, LIGHTS, LIGHTS. Can't say enough about light. Paint the room some bright, light color that will reflect artificial lights.