Okay, so what Roserade basically does is set up Spikes or Toxic Spikes and maybe put things to sleep. The specially defensive Spikes set is probably the most effective Roserade set I've ever used in OU as it stops Rain pretty well. It looks like this.
EVs: 252 HP, 120 Def, 136 SpD
Rest + Natural Cure makes for good recovery most of the time, surprisingly. Roserade also still has enough power to hurt stuff with Giga Drain and Sludge Bomb, although much of the time it will just be setting up Spikes.
There's also the more offensive Toxic Spikes set.
EVs; 252 SpA, 252 Spe, 4 HP
Blah blah, standard stuff. Pretty strong with a base 125 SpA stat. Good offensive Toxic Spikes user, and Sleep Powder is always useful.
As far as Roselia goes, it's actually pretty bulky on the special side with the Evolite. It also sets up Spikes and Toxic Spikes about as easily as its older sibling in OU.
EVs: 252 HP, 252 SpD, 4 Def
-Sludge Bomb/Toxic Spikes
Pretty much every set Roselia can (and should be) running all mixed into one. Sleep Powder is illegal with Spikes, so if you run Sleep Powder, run Toxic Spikes. Even though weather is much more rare in RU with the ban of Snover, making Synthesis much more reliable, I still find Rest + Natural Cure better most of the time.
So yeah, my two cents.