I need to make a ton of roses for decorations (like over 100) and was planning on doing it over a few weekends.  Some of the finished product is going to be shipped for gifts so I was planning on air-drying the flowers as opposed to freezing them so they will retain their form at room temperature and not smudge during the shipping process.  Because of this, I need something that would be stable over at least 2 weeks at room temperature, so I was thinking any type of butter in buttercream wouldn't work.  I also don't want them to taste gag-inducingly bad.  What do you guys think about the flavor of all-shortening "butter"cream versus that of royal icing?  The flowers will be small (think the size of a fingertip.)

I would use royal -- unless you use temperature sensitive packaging -- which really ramps up the price of shipping --

I definitely do not want to pay any more for shipping than necessary, so I will consider that!  Thanks!

I have used a crusting b'cream to make air-dried flowers for yrs.  You can use this recipe (note the crusting version at the end of the recipe).  Just let them sit uncovered at room temp - in a dark cupboard is great - for several days and they should dry just fine.  Roses take longer than other flat flowers.  Pipe them on a nail covered w/a small sq of wax paper or parchment. 

Bad old habit of mine......I didn't completely read your post.  All shortening b'cream is fine in certain situations:)  Just use a couple of tablespoons of flavoring.   Being that you plan to make such small roses it probably will not take but a day (24-36 hrs) for them to dry completely through.  As for shipping:  Pad 2 layers with much cotton covered w/paper or cloth.