This isn't enough for Roselia, let alone something as simple as a Caterpie.
Roselia will require about three times what you have here, a plot, adequate details and a bigger battle. You need to go beyond something more than "boy goes outside with his Pokemon and immediately finds the one he wants to capture" sort of thing, and you NEED descriptions here. You will want to describe your character, the settings, and not just put "It was his birthday. He went out and found Roselia hiding in the bushes." - You lack any sort of detail, and it is necessary for any story. You need to tell us what the forest is like, what the attacks used look like (does Thunder look like a shower of sparks? What does the main character and his Pichu look like?)
''Off course Ricky,Pichu is your's to take,here is his Pokeball the lightning ball''.
the adventure begin's.
What happened during the time that he got Pichu? Did he go to sleep, or go somewhere? You really cannot tell, and you need to do that for your readers. It's a confusing mass of words now, really.
Look at all the stories posted here as examples, because that is what you need the most help on. This is simply too short, and it lacks a little bit of everything. Practice, check your spelling through MS Word or some other document, and edit this with a more detailed story. Check out the << How to Write Stories >>
thread for more information on all this.