After the post concrete set up, I added the outside beams.  They were carefully leveled at one end, then each subsequent beam lined up and leveled at the other end.  This was done all the way around, so that when I came back around to where I had started, it was off by six inches!  I guess my level was not accurate enough.  Never the less, after a bit of eyeballing and tinkering, it all worked out.  I also cut the posts down to level.  The plywood flooring can now be added, and wiring placed underneath.  Then I get walls!