Ah the roaming legendaries... good times.. goood times.
Now, if you've ever read my post in the fav legendary thread, you'll know about how I encountered Raikou. But, I'll tell you anyhow 8D
Raikou was an odd one for me. He was the first legendary dog I met in Silver, then the first in Crystal, both within the routes between Ecruteak and Olivine. He was also the first I found in Soul Silver. I encountered him three times in Soul SIlver before Entei even came up. Afterwards, I captured him with a Fast Ball back in the same route I first met him in, which was, again, that route between Ecruteak and Olivine.
However, I have an amsuing story for the Latios in Ruby I dealt with.
In my Ruby, I encountered Latios right in the first route. Now, I wasn't exactly familiar with Latios yet, and I just thought he would stay there. So, I send out my Breloom to Mach Punch it. HOWEVER, it ran away after I hit it. Next time I encountered it was out in the Oceaninc routes between Pacifidlog and Evergrande, where my Dusclops managed to put it to sleep. IT FRICKEN' RAN AWAY!! Then, I encountered it in the forest route leading to Fortree. I managed to get Sableye to confuse him, but he ran away again! Finally, I encountered the fellow near the abandoned ship, where I cut him off with Crobat's Mean Look. I threw I don't know how many Ultra Balls with it on 3 HP. Then, I finally caught it with a Timer Ball. I wanted to nickname him "Scaredy Britches", but it wouldn't fit. So, I just left his name alone.