The poison is only a temporary solution. Roaches can reproduce extremely fast and in doing so change their DNA to become immune to posions.
Here is a fact about German roaches:
Females produce one egg capsule every 3-4 weeks. Each capsule contains 25-45 eggs. The female will carry the egg capsule with her until it is ready to hatch. The young(nymphs) will be able to breed in as little as 36 days.
1 roach can have 30 babies a month, assuming half are female, that's 15 more reproducing roaches a month.
1 roach = 15 reproducing roaches per month.
those 15 will have 30 each, again assume only half can reproduce.
So those 15 will have 15 each, and they will have 15 each...
all the while the first roach is still making 15 more reproducing every month...
Good luck trying to kill them with poison. You'll only end up helping them to adapt.
Your best defense against roaches is cleanliness. The less they have to eat (like bread crumbs or any crumbs for that matter, grease on the stove, and even cardboard) the better chance you'll have against killing them. Also eliminate as much moisture and water that you can. They'll drink water condensation off your refrigerator coils if you let them.
They can survive for a week without their heads. The only reason they die is because of dehydration. They can go a month without food. In a nuclear attack they'll be the only survivors because their exsoskelatal structure makes it difficult for the bright ultraviolet and radio active waves from penetrating into their bodies. And then they'll breed to become immune to the fallout.
Pretty fuckin' bad ass if you ask me.