Who do I call to block entrances on my house so those big water bugs/cockroaches won't get into my home?

I have a problem with those big waterbugs/cockroaches because I live by a ditch that goes around my house. I notice that when my neighbors spray for bugs, them seem to migrate over to my house. I think they are coming in through my vents and I think they are getting in from the top of the roof of my house. Who do I contact that will check every possible area where they(the bugs) can enter, the exterminator? a repairman? who?