What area of the US are you in. German cockroach control can be a huge challange. The enviromental conditions can sometimes make a simple treatment w/ insecticides of any type pretty useless. Glad to help bes I can, give me some idea of the where, how and why and lets see what we can do.
firstly i would recommend getting a good professional company to deal with it as they can be quite difficult to rid,
i have used a gel baised insecticide called goliath gel with good results against german cockroaches.
like the other guys said it would prob be better to get the experts in, save you time and prob a lot of money in the long term, but hey.. theres a tip any way!