Your boards are more likely to shrink than expand as they dry out
inside the house.

I always use screws as you can remove them without smashing the wood.
Buy an electric screwdriver and a good selection of cross point screws.
I only use nails for things like door facings and skirting boards.

Drill a pilot hole through the floorboard first, make the size very
slightly smaller than the shank of the screw. If after you've removed
the screw several times the hole in the joist is too big, then plug it
and re-screw as before. Far better than nails.

Chris.