For the flooring, I'm using a double layer of OSB boards, screwed to 2x4 floor beams set 15 inches to centers. This will make it difficult to do deep sky work as the act of walking will likely cause the floor to flex sufficiently to move the telescope off-target. It will mean sitting perfectly motionless during exposure time or, more likely, exposing while standing outside the building. I am working on a plan to make that possible. And should I ever decide to put in a permanent pier, it will be fairly simple to remove part of the flooring to set one in. The pier is the preferred way to go for most people, but not in this case. More on that later as the observatory project continues ...

UPDATE:
Now, nearly a year later, I'm planning on ripping out the floor, augering a deep hole and constructing a permanent pier for the telescope.