Careful with the poison. Try and find where they're hiding to better anticipate the poison's consequences. Last thing you want is for dying rats to crawl into hard to reach places and start rotting after a few days. Tearing open your roofing areas to pick out maggot infested rats ain't fun. Speaking from experience.
Depending on the severity of your infestation you could try traps. If you have many then poison is the only way to go, but if you suspect it's only a few then traps will probably be the option that gives you the most control.