If you know someone who's been especially good this year—and you're feeling very generous—you need to check out our roundup of prefab and DIY housing structures that you could gift this holiday. (And if you give one of these, you'll probably walk away with the best gift-giver award too.) Unlike other very generous gifts (car, anyone?), a house or fun dwelling can last forever and will, in many cases, appreciate in value. So while we doubt that many people put "tiny house" on their wish list…