According to Toller :
I am building a 4x8 tool shed. I have the 4 sides up, and must buy
materials for the roof and siding. I am not sure when I will get around to
doing that. If it rains now is the framing going to be okay, or should I
put tarps over it?

The framing will stand up to getting wet for a while, but if it's
too long, it _may_ warp in ways that make things difficult, and if very
long, it could start to objectionably weather/rot. Getting wet for a
week or two? Nothing to worry about.

More of a concern is plywood (eg: floor decking). If you have a
non-exterior grade plywood floor deck, if it gets really soaked, it may
start to delaminate/soften. If water doesn't puddle on the decking,
it'll handle a few rains without problem.

That said, when we had a "reconstruction" halt on our shed before
the roofing arrived, I did put in a tarp to protect the floor and
the plywood gussets on the home-made roof trusses.

On a related question, the siding is supposed to be installed with
galvanized nails. I hate to spend the money for them, since I have more
non-galvanized nails than I will ever use and would have to buy the
galvanized. How serious will the rust stains (I presume that is why
galvanized is called for, no?) be if I use regular nails? (upstate NY)

If, say, this is formed vinyl/aluminum siding where the fasteners are
hidden, it doesn't make much difference. I'd use galvanized hex head
socket-drive _screws_ and power drive 'em. It's not as if it's
a lot of fasteners.

If the siding is board type, _especially_ if it's a composite product
(weather proof MDF, aspenite etc) or pressure treated in some way,
galvanized is really essential. Modern PT (eg: ACQ lumber) aggressively
eats non-galvanized (or casually coated) fasteners just from atmospheric
moisture, let alone getting wet. You might not see any staining,
but the siding will start falling off. Perhaps as quickly as 3-4 years.

Composite materials less so, but still.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.