While it may be difficult to eliminate all possible foods on the outside of a structure the effort still can reduce the level of food available. Garbage cans can be kept clean, with properly fitted lids, and with plastic bags inside to contain and seal the garbage. Pet foods should not remain available outdoors. Harborage opportunities can be limited by removing all unnecessary clutter from the soil and stacking other things neatly off the soil on racks or boards, but not directly in contact with the dirt. Piles of yard debris should be removed regularly and the soil kept dry. Thick vegetation needs to be pruned up off the soil or removed, and branches touching the structure must be trimmed away. These steps reduce the attraction of a property and thus reduce the numbers of roaches that can survive there. It also minimizes the number of roaches that live close to the structure. Now, a careful inspection should also reveal many openings that would allow these roaches to enter the structure, and every one of these that can be permanently closed means less roaches getting inside, and you can focus insecticide applications around those remaining entry points. 

Within a structure dusts within walls work well, since roaches may hide within the walls during the day. Boric acid dust is good as are contact dusts like Tempo and DeltaDust. Liquid insecticides can be applied around travel areas and directly into likely harborage points, as this then puts the roach and the active ingredient together for the longest time. Microencapsulated products like Demand, CyKick, and others have the advantages of lasting longer, being less affected by moisture, and of attaching to the roach as it moves over the surface. 

Granular bait products also seem to be very acceptable to the larger roaches, and these may be applied into wall voids using a duster such as the Centrobulb, or used according to the Label outdoors in and around likely harborage points and travel routes. There also are many kinds of insect bait stations available if the bait needs to be kept in a more controlled manner, and these may be placed around the perimeter of the structure. The roaches may often be hiding outdoors in storm drains, under man-hole covers, under sewer vent covers, or in water meter boxes. These may be treated using a properly labeled contact insecticide, including some dusts. Be very careful, though, to read the Label to be sure the product is labeled for that site.