Standard disco is 1960mm to roof bars. Says so on the sun visor.
One thing to be mindfull off, I learnt this when transporting yachts, is that the barrier (or bridge clearance) is measured when installed, however the heights are rarely updated when resurfacing occurs.
Ripped a fly bridge off a 36" Broom cruiser many years ago. if that wasn't bad enough, i was transporting it back to the factory for repairs after it was struck by an oil tanker off the coast of Greece. To make matters worse the owner was following behind in a hire car and caught it on his bonnet.