You have to use a shiny stone on Roselia to evolve it. Unfortunately, you can't get shiny stones in sapphire, ruby, or emerald. You have to trade a Pokemon from diamond, platinum, or pearl into your game that is holding a shiny stone in order to get it. I know it sucks, but that's the only way I can think of to get it.
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Roselia evolves into roserade with a shiny stone.
in order to evolve Roselia you have to use a sun stone on it You use a shiny stone, not a sun stone.
All you need to do to evolve a Roselia is use a shiny stone on it. No trading, and it will never evolve on it's own no matter what level you get it to.
Shiny Stone
A Shiny Stone will evolve a Togetic into a Togekiss or a Roselia into a Roserade.