During the winter and early spring, we installed floor joists on 4 foot spacing and pine 3"x6" tongue and groove floor decking.  Here is Isa Radcliffe predrilling a 3x6 to accept a screw into a log joist.  She is kneeling on what will be the upstairs bathroom floor.

Here's the Loft floor installed  - now we need a stairway and railing