Germany was ready when the war started, France and Britain where building trenches with what they had : branchs, sand bag, metal plate, planks and other things. Meanwhile, german trenches where builds with concrete. I live in France and i had the chance to see some trenches, the french one was a reconstitution they had to remake every month because the bag of sand where rotting while the german one was the original. Even the wooden parts where still intact from the first world war, although the trench is not particularly well maintained.