As a 3rd generation Texan (and very happy transplant to the Pacific NW:D) I have WAY too much experiece with roaches!
Boric acid has never worked all that well for me, maybe I didn’t use enough of it.
But then, I tried the “diatimatious(sp?) earth” solution for fleas once, too, supposed to work on the same principle…LOLLOLLOLLO…sigh…NO. Now, the flea traps made of a gallon plastic water or milk jug and a nightlight and sticky paper? EXCELLENT!!! 
The only things I have found that really worked for roaches were those traps/baits and or sprays (I always avoided sprays) which contained a hormonal ingredient which sterilized the critters. You set them out and after a while you start to see roaches with withered wings and other deformities…soon, all gone. Not sure what the ingredient was, but it was in some RAID baits I used to buy. Don’t even think it killed them, just rendered them sterile.
I admire roaches, I really do. They are amazing critters and they have their place in the universe…it is just not in MY HOME! :mad:
I despise the big flying ones, but they always tended to be less of a problem wrt infestation. They would come in, esp. during fluctuations in the barometric pressure/thunderstorms, and fly around, freaking me out, and then as suddenly retreat back to the great outdoors.
They are hardy buggers, though…I once stepped on one while walking on a Houston street one night, after doing my best to avoid doing so, and the damn thing SQUOZE right out of its skin and continued running around skinless, a white cockroach…EEEWWWWW!!! :eek: I’ve also witnessed headless ones go on living for days.
But, the OP mentions GERMAN cockroaches, the much smaller ones, and THOSE are the fuckers you gotta come down on hard…they will infest your digs like zombies in a brain factory (yeah, yeah, I know, terrible, whatEVER, I’m making an important point here :rolleyes:) The big ones have a bigger ick/show factor, but it is the smaller ones who really pose the threat.
Even living in climates where they are not common (Colorado, Portland, Or) you see them from time to time. They come from other areas in boxes and other items, often as eggcases, and proceed to infest their new digs. They move readily from apartment to apartment, house to house, and if your new neighbors are from florida or texas or mexico or any other area where they are ubiquitous, be vigilant.
Rule #1: KILL THEM IMMEDIATELY!!! Seriously. If you have to break every dish in the kitchen to do it, kill the little fucker when you see it. Do NOT let it escape to breed/eat again! Since living in this apartment (3 yrs) I’ve seen only 3 or 4 and killed them all…they were NOT, I expect, expecting ME when they crept in looking for a snack. 
Rule #2: Leave NOTHING out for them to eat. They are drawn to scraps or even unwashed counters like a magnet to steel. Seal all your food up in glass or plastic or refrigerate immediately (something I got used to in Texas, since sometimes the damn things would rush out and try to grab something while I was cooking/cutting it and certainly within a few minutes of the kitchen being vacated.)
Rule #3: If you see more than a few in a short time period, get thee to the store and get some sort of poison or trap to set out. Don’t wait.
My sis-in-law once moved from Texas to Portland to live with us for a while…within a month of her arrival (boxes, etc in tow) we were completely infested with German Cockroaches. I walked into the kitchen late one night, turned on the light, and the white floor was covered with little brown, fleeing bodies. :eek: Had to fumigate the house TWICE to get rid of them. AND be vigliant about killing any strays we saw for months.
Just a word to the wise, if you see a German cockroach in your home, regardless of where you live, kill it if you can and take precautions immediately or prepare to have a much bigger problem on your hands soon.