Finding extra seating or sleeping space is a challenge for most homeowners.  Kids' bedrooms are unlikely places for guests and even the occasional slumber party with space being at a premium.

A window seat is ideal for bedrooms, creating a nice space to fill in between windows, with extra seating and storage below.  You can take that concept one step further by putting the storage space below the seat to a dual purpose.  Add wheels to a pull out drawer and a drop down cover over the drawer and a fold out cushion, and you have added a fun space for an overnight guest of nearly any age.  Teens in particular have limited space in their bedrooms for overnighters, having outgrown the bunk bed stage, so this might be just the ticket.

In a family room or even living room, this idea can be adapted to any style you happen to enjoy.  By keeping a window seat trimmed out in a similar wood and style to the rest of your furnishings, it will go unnoticed as a bed, until the time you need it, making a permanent addition to any room and added value at resale time.

You can make any wall "window seat ready" by simply adding some bookcases to either side of a window and thus creating a space for a window seat.  By adapting the seat part of the box into a rolling drawer, you will have both storage and extra seating.  You can have cushions made to fit, or make your seat in the dimensions of a fold-away mat that can be stored inside the drawer/seat along with the linens and pillows necessary for a comfortable night's sleep.

Bedrooms and family rooms, even more formal living rooms are all good places to re-think extra seating and sleeping space.  If you happen to have a very small space, you may have to really think outside of the box for additional, occasional sleeping space; think kitchen banquet.  While not ideal, if you are really cramped for space and have occasion to host overnight guests, this is an area you cannot overlook.

Think of campers and motor homes.  The kitchens in these spaces have a table that will rest on angle iron brackets when the center pole is removed, and the cushions will serve as a mattress for the night.

There are lots of ideas for making good use of small spaces; you just have to be a bit creative and willing to find them.  Recreational vehicles are great places to look when you need to maximize space.