There's so many options to structure in writing music or melody. From my own experience having scribbled down hundreds by now over the years I always wait for that moment when the tune or rhythm tells me how I will begin a piece; maybe 4/4 or perhaps cut time [2/2] time. Of course for jigs and like 6/8 is oft used in folk music as well.
Then there's various other options, and some rarely used or met with on some music at least; I am thinking of the strange 5/4 beats to rhythm, and that one extra note in bar that makes it surprisingly different in affect.
I wonder what is the most unusual structure to use, or that you come across, for all the rest of you out there in 'free reed' land? I suppose they all represent a challenge, to a degree, depending on how they are presented on the page.
For those that do not read music - don't worry; you will have all that rhythm built in as well a part of your instinct.