If you're cold, they've got to be cold too, right? The responsible thing to do is to bring them inside. Actually, most spiders overwinter in egg sacs or as juveniles underground, under rocks, or under bark, while some are active through the winter.
Important note about colors — Each brand of shirt comes in several colors. The drawing is printed in black except on some children's shirts. Please be careful not to order a black print on a dark-colored shirt, as the print may be hard to see.