I want to the stripes for the flag (on fondant) but don't know how ....do you make your own stencil? or is there another way to do this

Are you doing buttercream? Could you do the red stripes in fondant? That might give you the cleanest sharpest contrast for the stripes. http://www.usflag.org/flagspecs.html will show you how to do the measurements if you really want to be accurate. Not too accurate though, I'm told you can't copy a flag exactly for any purpose other than a flag. Probably more info than you needed or wanted...

Maybe I'm not understanding but you could just use a ruler and pizza cutter and cut your stripes and lay them on the cake.

Hi Charmed, I just made a flag cake last night. This is an Idea if you are using fondant to cover your cake. I used a Fondant Ribbon Cutter. It makes perfect stripes. First I covered my cake in white fondant, then added red stripes going across and down the sides. I also used to Gum Arabic (Edible Glue) to adhere the stripes. then I pushed down the stripes a little to mold them to the white fondant.
Hope that helps.