where can i find latios and latias in pokemon ruby?

Answer 1

You can only catch Latios after you the beat the elite 4. The location of it is random and you have to keep looking for it everywhere including grass, tall grass, dessert and water. Once you find it, it will behave as the legendaries dogs in which it will run away when it can if you are not fast enough. I recommend you to use your masterball on it.

Answer 2

You only catch Latios in Ruby, it is a migrating pokemon, and will be found over the water. The best method of finding him is by haveing a lvl 45 pokemon first in you party, and using super repels, surfing between two water routes.