For those building in cold hangars, take heart. Our project finally flew a couple of weeks ago. For the first flight I set minimum weather limits at -15C and 10kts of wind. We managed to get up to -15C and the wind dropped to less than 10kts so we were a "go" for first flight.
The flight was particularly sweet, given that much of the work on the aircraft had been accomplished in a hangar which isn't much more than a shed, with snow blowing in, no insulation, no ceiling, and a foot or so of open space under the sliding doors. After a half dozen winters of this I figured she had to fly before I went through another winter of frozen fingers.
Keep pounding away on rivets - it's all very worthwhile when you get to taste the sweetness of flight.