Instructions
Travel to Route 34 and look for a house with a fence and a man in a small room to the left of the fence. This is where you breed your Pokemon.
Speak to the woman at the desk inside the house. She will ask you whether you want to place any Pokemon into day-care.
Select Roselia and a compatible Pokemon to be entered into day-care.
Leave the house and then immediately re-enter it.
Speak to the man outside the fence; he will tell you whether your Roselia and her potential mate like each other enough to mate. If they do not, the man will state that ̶0;they want to play with others.̶1; If this occurs, repeat the process outlined in Steps two through four, and speak to the man again.
Leave the house, walk exactly 256 steps and then return to the house.
Speak to the man outside the house and see whether your Pokemon have finished mating. If they haven't, leave the house, walk exactly 256 steps and return to it again. Repeat this process until the mating is successful.
Enter the day-care center and collect your Pokemon egg once the mating is complete.