The cartography expert is planning to move into a new base later this year and work on the project remains on schedule.
This is despite the extreme weather conditions which seriously disrupted the country earlier this month.
Chief executive Vanessa Lawrence was on hand to witness the completion of the external structure and joined the builders from developer Kier to add the finishing touches to the roof.
She was handed a commemorative concrete trowel after receiving her taste of life as a construction engineer.
"I am looking forward to moving into Ordnance Survey's new home and seeing our staff settle in and enjoy their new working environment," Ms Lawrence commented.
She added that the building will be a modern and dynamic structure that reflects the group's world class business.
The roots of Ordnance Survey can be traced back to the late 18th century, although the first recorded use of the name did not take place until 1810.