Walls and Ceilings - converting upstairs family room

I would like to convert an upstairs family room to a bedroom. This would mean building up a half-wall, and installing a door. There is also a 10x10 room that would be included in this new room, which I would convert to a closet/dressing room (it is pretty big, my office now). Is this easy to do? Is there a way to convert the room and not loose the upstairs natural light in the stairway? The master bedroom is now on the main level of our 2 story house. I plan on moving it upstairs, and converting the now br into the living room. All this because we have no coat closets, and the only main floor bathroom access is right through my bedroom (a real pain when we have company over). Does this sound do-able? Has anybody tried this type of project?
Thanks!

Two things define a good bedroom. A closet and access to a bathroom, besides adequate room for a bed. Consider your resale value once these modifications are made. Will they enhance it or detract from it?
I don't understand your "half wall", what is that? Not sure about losing your natural light, but that is why the window manufacturers are in business. You can always add light.