shirring help? MY FIRST GIVEAWAY!

Ok, so I know people are crazy about shirring, and I also know that I'm a coward. I need to jump on the bandwagon. I want to jump on the band wagon. But I'm scared!
Today, I saw this shirt at Ann Taylor Loft (click the link for the better picture on the ATL website. Obviously I took my picture through the window ... while pushing a stroller...). I'm a totally sucker for Swiss Dot. Swiss Dot and Seersucker. (I think that means that I love summer?) Anyway, I crave this shirt. In BRIGHT yellow. Granted, it's on sale now, and probably costs less to buy pre-made than it will for me to buy Swiss Dot (in aqua!!! or lime!!! or white with red dots (my FAVE!!!)) , but since I took the wardrobe refashion pledge, I cannot buy it!!! (ok, actually, now that I look online, I'm guessing that it's gonna be even harder for me to make it... I can't find any good colors! I'm gonna have to buy white and dye it. Dye-ing is another secret fear of mine.)

Therefore, I MUST figure out how to MAKE it for myself.
But I need help, Oh Blog Readers of the World.

I looked at the shirt online in detail, and I think it's made of two pattern pieces. One piece for the front and back, and one curved piece for the strap. so I know the shape I want to cut the pieces. HOW MUCH BIGGER DO I CUT THEM!?!?!? 1.5x? 2x? how much fabric does shirring take up?
PLEASE give me a ballpark before I start cutting with abandon tomorrow???!?!!???! (also, please DON'T tell me what Bernina told me about my fancy ruffle foot (~"there are no guidelines, every fabric is different, you just have to take a yard of the fabric and experiment till you get the ruffle density you like.") There MUST be a general rule of thumb for shirring.
SO. As incentive:
I'll do a random # drawing on Monday night, and the winner will either get a Reversible Bean Dress/Top
or a giant box of crochet thread. LOTS of great colors. (by giant, I mean, 12"x12" overflowing). My wonderful mother got me the box at least a year ago, and I had big plans, but now... it's still just sitting there in the closet, taking up room...
So my first givaway is officially comencing NOW.