After competing with the rain, my father and I finished sheathing the subfloor with 1/2 inch ply, Because of the odd spacing of the floor joists I needed 7 sheets for a 6 sheet job, but I will be using some of the extra for my window/ door headers and my dad already used some of it on another job.
Note about tarps. Definitely go with the more expensive sort... I went through one in only one storm. Now that I've switched to some heavy duty visqueen it has lasted through a number downpours. I plan to invest in a much larger tarp to help cover the walls once they are up.