Garry, My wife and I have a plan in mind like yours when/if we can make a move from the city in a few years. My thinking is that unless you have a planned need for the upper level area of the barn, after you have the house, it would be a lot cheaper to do like Alan has done. Regardless of how large of barn you want to end up with it would not be hard to partition off a section for living even if the partition were to be removed in the future. A two story barn is going to raise the construction cost considerably and most likely some of the code issues will become more involved. Your plumbing needs would be at ground level and could be positioned to leave a bath in the barn if the living space is returned to barn space in the future. I am sure things differ by region, but I know I could build a one story pole barn cheaper than a two story barn of the same square footage in our area.
MarkV