The intention to kill is what Buddhism focuses on. There are times in normal lay people's lives that: they may need to preserve a building, they may need to protect their pets, they may need to save their own child from worms. They give the child one little pill, and believe me it's one of the tiniest, tiniest pills I've ever seen, but it actually kills the worms in the intestines, and saves a person's life. When your intention is actually something different, something to help out of compassion for some other reason, then if you have to kill the cockroaches or the fleas or whatever, then at least your intention is in the right place.
This is something we ourselves have to do here at Wat Kow Tahm because the wooden buildings get little borers in them, which destroy the wood, and if they are left alone then the buildings fall down. So we teach the assistants to do a Compassion/Lovingkindness wish for the borers before they do the spraying. We also try to protect the buildings beforehand so that this doesn't need to be done. That's why you notice on the wooden buildings that there are black wraps around the base. These create a physical barrier, which prevents termites from getting up so that we don't have to kill them. We would love to be able to prevent a lot of this by rebuilding all of the dormitories out of concrete, that would help prevent almost any problem. They still might go into the roof, but not as easily.
To prevent having to kill is what we would like to do. If we have to do it, we do it, but the intention is not really to kill. The intention is to preserve the buildings so that people like you can learn the Dhamma. If we had tons of more money, then of course we could replace them all, and we would do less killing here.
That's something for you to consider in your own life, prevention is better. Can you do something to help prevent your cats and dogs from getting fleas? Wash them, clean them, whatever. I don't have a dog myself, nor a cat. Is there something that has been created to make the dog smell in some way, or whatever, so that the fleas don't actually go on them? Can you take care of your house so that you don't get so many roaches?
So if you can, try to prevent. If you can't, try to have the right intention, if you have to do something like that.