I would think about how you want to use the room, how you want to arrange furniture, what you want the focal point of the room to be. Can you share a floor plan?

we don't have a separate family/living room. We have "flex" space room which we are using as a play room for our kids off the kitchen (14x13). So this is our main living space.

Very helpful! We can better picture your situation now.

Gosh, that is tough, because I can see the pros/cons to both. Do you have views out the back if you kept the tall wall full of windows? Which direction would that face? We have friends with a cathedral living room, and they always have the windows covered because it faces west. The light is too instense to comfortably keep the shades open, and the room gets crazy hot no matter what they do. Something to consider. I usually always vote for more windows and natural light, but it all depends. How many windows would you have on the shorter wall if you moved the tv and fireplace to the long wall?

Since the T.V seems important I would think about where that goes and your seating needs and also how to control the light from all the big windows when you want to watch T.V

I think if we do TV on fireplace on the high wall with surround windows, we have more options with furniture... Is 13 ft to narrow for this room? Should we pay more and have this room bumped to 15 ft wide?

If you have room in your budget, I would absolutely bump it out to make it a few feet wider........I think 13' can feel narrow, especially when entertaining. Although the narrower room would still work in your home, because you don't have doorways, stairs, walkways, etc on the other side of the living room. I have just found that having closer to a square shape is easier for arranging furniture and having some space. Is there a completed home near you with this layout that you could walk through and get a feel for?

This old thread might help as you think about it:

http://ths.gardenweb.com/discussions/2686882/what-size-living-family-room

thanks everyone, we decided to extend the room's width by 2 ft to make it 15 ft wide. I am hoping the extra 2 feet make it feel less narrow.

do you think 15 ft is big enough?

Our living room is 15x17 and is comfortable for us, but we never have big groups over, and the size is proportional to the rest of the home. What will the overall square footage of the house be?

I think that would be big enough, but it is just my preference/opinion......our house is 3000 sq ft and 15 x 17 is just about right. I wouldn't mind it a little bigger just to have more waking space behind the couches. But it all depends on the layout and your furniture and how much space you will need for entertaining. That said, you don't want it so big that it feels like a basketball court or "not cozy" when you don't have people over. I think it was a good idea to widen to 15 feet.....it will feel better for you and give you more flexibility with furniture. What is the size of your current living room? Maybe that will help guide you re: ideal living room size for you. 15 feet wide woud be "big enough" for me, though. :-)

You can have both, fireplace and windows, it would look sharp on the wall like this and it will make a real focal point. I would consider doing something like this, but any window configuration will work.