I'm making a stack of presents cake this week, and I want to do this effect with the bottom cake (9x13x5). I've searched the net and can't figure out how they got the stripes so smooth. Do you think it's painted on, or strips cut and placed next to each other and rolled gently (although whenever I do that my stripes go not as crisp and clean after rolling, unless the fondant is about 1/3 inch think, which is too thick to try to cover a cake with)? Is it another technique?
That looks like modeling chocolate - fondant doesn't usually allow that kind of control.
I've never tried working with modelling chocolate yet, how would I do this with modelling chocolate?
I just googled Baking Arts, the people who made the cake in your photo, and they sell two books on making gift wrapped cakes and stripes. A little experience under your belt working with modeling chocolate might not be a bad idea. Maybe take a modeling chocolate class or get the books? There's a bit of a learning curve getting used to working with it and this project seems a little ambitious for your first foray into modeling chocolate. Others may disagree.
ACraftsy has a class conducted by Marina Sousa, Advanced Fondant Techniques, and she does a similar box. Her striping method actually seemed pretty easy. Their courses are often on sale and might be worth a try.
The cake in your photo is definitely modeling chocolate. Baking Arts does sell the DVD for this technique. You can also purchase the class online at Cake Masters. Richard Festen is the instructor. You will need a stand mixer with pasta roller attachment to do this. You can register at CM for free and just pick and choose the class you want.
The Craftsy class doesn't show how to get the sheet, it just shows how to do stripes, and slightly wonky ones at that. If you get the class from Baking Arts you'll be able to do it, it takes time and patience but it works well. It's definitely modeling chocolate, fondant won't smooth into itself the way that it needs to to get that smooth surface.
If you don't care about getting the super-flat surface, though, just roll out a sheet of fondant and apply thin strips of fondant to it using a ruler to keep them straight while you line them up.