Can I freeze buttercream roses. I am making several cakes for a 50th birthday party and would like to make the roses ahead if possible. I thought someone told me that you could freeze them but am not sure.

Yes but the heat of your hand will casuse them to melt instantly upon removal.
Why not air-dry them? Just let them is UNcovered, NOT in the frig or fzr for at least 12-36 hrs.
Use a b'cream recipe that has very little fat and extra cornstarch in it.
I can't remember, but I might have posted my recipe for air-dried b'cream on this site. Try a search for it.

They could droop when they thaw.

It's best to let them air dry completely. They'll be easier to handle and place where you want on the cake because they'll weigh less without the moisture. You'll be able to stick them on the sides without fear of them falling off.