I need the best recipe for buttercream for roses. Mine tends to be droopy

If they are droop your icing probably isn't stiff enough.

I use the regular Wilton stiff buttercream for my roses.

You can use whatever buttercream recipe you'd like, just add more powdered sugar to it until it's a stiff enough consistency to hold up the petals so they aren't droopy. Good luck.

The all shortening buttercream recipe is great for roses but not good for eating