Small Spaces Bookshelf

I have been living in small spaces since I went to college.  After college I moved to NYC and eventually settled in to a 200 sq. ft. apartment with a roommate.  The kitchen was so narrow at points, that two people couldn't walk by the stove at the same time.  I'm now in CA, but we still have a smaller space and need to conserve space and make all the furniture in the living room moveable so it can work for many different situations.  That's where this sweet moveable bookshelf comes in.  The how-to blog uses two pieces of wood braced together, but you could also just buy one of those cheap shelves at ikea or a hardware store and only have to add the casters.  It just depends what look you're going for.