That depends on what you mean by "work." The length, as Kiteman said, determines the note -- specifically, the length is half the wavelength of the fundamental frequency. If you want a particular note, then you need to make it the right length or it won't "work" the way you want it to. If you're trying to build a flute, with finger holes to generate different notes, then you need to get both the length and the spacing of those holes correct. Look up a basic text or article on "woodwind instrument making" via Google. Such articles should include the basic physics you need for standing waves in air.