A roth IRA is not necessarily a bad place for the money, but there are more rules to the distributions than you listed. First, you can withdraw money that you put in to a roth as a
contribution at any time without penalty. You run into weird rules when taking distributions of
earnings early though.
Also, the qualified distribution exception for a first home are capped at $10,000, so be aware of that.
If you want to go that route, you might be able to save yourself a little bit of money on taxes in the next few years, but it's not a strategy that you could use for the entire down payment, (unless it's a small house or a cheap area). Also remember that you can still contribute to your Roth IRA for 2013 up until you file your taxes.
Before you go this route, read up a little more on Roth IRAs just to be sure it's what you want to do and that you've got the math all worked out.
Check out
http://www.investopedia.com/articles/retirement/03/030403.asp for a little bit about it, or if you're ambitious and can stay awake reading the tax code,
http://www.irs.gov/publications/p590/index.html.