To begin with, we checked the joists for any crown and hand-planed them to level, so that the decking would sit nice and flat. Vince became a pro at this job.
Now to install the decking: John and Brune (a volunteer from France) set a 2x2 along a stringline, working together to predrill and drive the decking screws.
Here, Brune and Vincent take a rest at the edge of the floor deck. The pattern of 2x2's and 2x4's in the floor deck will align with the pattern of the wall studs and the voids between them.
Below, the completed floor deck...
... already a satisfying platform for viewing the landscape.