The biggest cockroach I ever saw was in BKK in 2013 when we were staying for a couple of weeks in a 1-room bit of a rather downmarket block ... A roach the size of a mouse ran out one day from under the bed.
I thought that was the roach of roaches but, as I see above, apparently not.
Here at home in south Surin I see about 2 or 3 every week, 'normal' size, but only if I haven't renewed the anti-gecko/snake spray ...